diff --git a/backend/.env.example b/backend/.env.example
index faad37a..4362e64 100644
--- a/backend/.env.example
+++ b/backend/.env.example
@@ -3,3 +3,5 @@ KF_OJ_LOG_LEVEL=INFO
 # Optional until database-backed use cases are implemented.
 KF_OJ_DATABASE_URL=postgresql+asyncpg://kf_oj:local-dev-only@127.0.0.1:5432/kf_oj
 KF_OJ_AMQP_URL=amqp://kf_oj:local-dev-only@127.0.0.1:5672/kf_oj
+KF_OJ_BROWSER_ORIGINS='["http://localhost:5173","http://localhost:8000"]'
+KF_OJ_SESSION_LIFETIME_SECONDS=43200
diff --git a/backend/pyproject.toml b/backend/pyproject.toml
index 949761d..68a991a 100644
--- a/backend/pyproject.toml
+++ b/backend/pyproject.toml
@@ -17,9 +17,11 @@ dependencies = [
     "asyncpg>=0.30,<1",
     "alembic>=1.15,<2",
     "aio-pika>=9.5,<10",
+    "argon2-cffi>=25.1,<26",
 ]
 
 [project.scripts]
+kf-accounts = "kf_oj.modules.identity.cli:main"
 kf-learning-worker = "kf_oj.workers.learning:main"
 kf-outbox-publisher = "kf_oj.workers.outbox:main"
 
diff --git a/backend/src/kf_oj/api/app.py b/backend/src/kf_oj/api/app.py
index 0d6d81c..695658e 100644
--- a/backend/src/kf_oj/api/app.py
+++ b/backend/src/kf_oj/api/app.py
@@ -2,11 +2,17 @@ import logging
 from contextlib import asynccontextmanager
 
 from fastapi import FastAPI
+from fastapi.exceptions import RequestValidationError
+from starlette.responses import JSONResponse
 
 from kf_oj import __version__
+from kf_oj.api.body_limits import BodyLimitMiddleware
+from kf_oj.api.v1.identity import router as identity_router
 from kf_oj.api.v1.router import router
 from kf_oj.core.logging import configure_logging
 from kf_oj.core.settings import Settings
+from kf_oj.infra.db.session import build_engine, build_session_factory
+from kf_oj.modules.identity.service import IdentityService
 
 
 def create_app(settings: Settings | None = None) -> FastAPI:
@@ -17,20 +23,37 @@ def create_app(settings: Settings | None = None) -> FastAPI:
         configure_logging(settings.log_level)
         logger = logging.getLogger("kf_oj.api")
         logger.info("Platform API started")
+        engine = None
         try:
+            if settings.database_url is not None:
+                engine = build_engine(settings)
+                app.state.sessions = build_session_factory(engine)
+                app.state.identity = IdentityService(
+                    app.state.sessions, lifetime_seconds=settings.session_lifetime_seconds
+                )
             yield
         finally:
+            app.state.identity = None
+            if engine is not None:
+                await engine.dispose()
             logger.info("Platform API stopped")
 
     app = FastAPI(
         title="KF-OnlineJudge Platform API",
         version=__version__,
-        description="工程骨架。当前只提供进程存活检查，业务接口逐项实现。",
+        description="平台 API。身份使用真实可撤销会话，业务接口按模块逐项接入。",
         docs_url="/api/docs" if settings.environment != "production" else None,
         redoc_url=None,
         openapi_url="/api/openapi.json" if settings.environment != "production" else None,
         lifespan=lifespan,
     )
     app.state.settings = settings
+    app.add_middleware(BodyLimitMiddleware)
+
+    @app.exception_handler(RequestValidationError)
+    async def invalid_request(_, __):
+        return JSONResponse({"detail": "invalid request"}, status_code=422)
+
     app.include_router(router, prefix="/api/v1")
+    app.include_router(identity_router, prefix="/api/v1")
     return app
diff --git a/backend/src/kf_oj/api/body_limits.py b/backend/src/kf_oj/api/body_limits.py
new file mode 100644
index 0000000..ea65bc1
--- /dev/null
+++ b/backend/src/kf_oj/api/body_limits.py
@@ -0,0 +1,63 @@
+"""Bound request bytes and upload time before schema parsing can allocate large inputs."""
+
+import asyncio
+
+from starlette.responses import JSONResponse
+
+
+class BodyLimitMiddleware:
+    def __init__(self, app):
+        self.app = app
+
+    async def __call__(self, scope, receive, send):
+        if scope["type"] != "http" or scope["method"] in {"GET", "HEAD", "OPTIONS"}:
+            await self.app(scope, receive, send)
+            return
+        limit = 8192 if scope["path"] == "/api/v1/auth/login" else 1024 * 1024
+        headers = dict(scope.get("headers", []))
+        length = headers.get(b"content-length")
+        if length is not None:
+            try:
+                size = int(length)
+                if size < 0 or size > limit:
+                    raise ValueError
+            except ValueError:
+                await JSONResponse({"detail": "request body outside byte policy"}, 413)(
+                    scope, receive, send
+                )
+                return
+        # Buffer a finite body so errors can be returned before response headers are sent.
+        chunks, size, received_chunks = [], 0, 0
+        try:
+            async with asyncio.timeout(10):
+                while True:
+                    message = await receive()
+                    if message["type"] == "http.disconnect":
+                        return
+                    body = message.get("body", b"")
+                    size += len(body)
+                    received_chunks += 1
+                    if size > limit or received_chunks > 1024:
+                        await JSONResponse({"detail": "request body outside byte policy"}, 413)(
+                            scope, receive, send
+                        )
+                        return
+                    chunks.append(body)
+                    if not message.get("more_body", False):
+                        break
+        except TimeoutError:
+            await JSONResponse({"detail": "request body deadline exceeded"}, 408)(
+                scope, receive, send
+            )
+            return
+        body = b"".join(chunks)
+        delivered = False
+
+        async def bounded_receive():
+            nonlocal delivered
+            if not delivered:
+                delivered = True
+                return {"type": "http.request", "body": body, "more_body": False}
+            return await receive()
+
+        await self.app(scope, bounded_receive, send)
diff --git a/backend/src/kf_oj/api/dependencies.py b/backend/src/kf_oj/api/dependencies.py
new file mode 100644
index 0000000..8acb089
--- /dev/null
+++ b/backend/src/kf_oj/api/dependencies.py
@@ -0,0 +1,50 @@
+from typing import Annotated
+
+from fastapi import Depends, HTTPException, Request
+
+from kf_oj.core.settings import Settings
+from kf_oj.modules.identity.public import AuthenticationFailed, Principal
+from kf_oj.modules.identity.service import IdentityService
+
+SESSION_COOKIE = "kf_session"
+
+
+def identity_service(request: Request) -> IdentityService:
+    service = getattr(request.app.state, "identity", None)
+    if service is None:
+        raise HTTPException(503, "identity service unavailable")
+    return service
+
+
+def trusted_origin(request: Request) -> None:
+    settings: Settings = request.app.state.settings
+    if request.headers.get("origin") not in settings.browser_origins:
+        raise HTTPException(403, "request origin rejected")
+    if request.headers.get("sec-fetch-site") == "cross-site":
+        raise HTTPException(403, "cross-site request rejected")
+
+
+async def current_principal(
+    request: Request, identity: Annotated[IdentityService, Depends(identity_service)]
+) -> Principal:
+    try:
+        return await identity.authenticate(request.cookies.get(SESSION_COOKIE))
+    except AuthenticationFailed:
+        raise HTTPException(401, "authentication required") from None
+
+
+async def unsafe_principal(
+    request: Request, identity: Annotated[IdentityService, Depends(identity_service)]
+) -> Principal:
+    trusted_origin(request)
+    try:
+        await identity.authenticate(request.cookies.get(SESSION_COOKIE))
+    except AuthenticationFailed:
+        raise HTTPException(401, "authentication required") from None
+    csrf = request.headers.get("x-csrf-token")
+    if csrf is None:
+        raise HTTPException(403, "request token required")
+    try:
+        return await identity.authenticate(request.cookies.get(SESSION_COOKIE), csrf_token=csrf)
+    except AuthenticationFailed:
+        raise HTTPException(403, "request authentication rejected") from None
diff --git a/backend/src/kf_oj/api/v1/identity.py b/backend/src/kf_oj/api/v1/identity.py
new file mode 100644
index 0000000..4000823
--- /dev/null
+++ b/backend/src/kf_oj/api/v1/identity.py
@@ -0,0 +1,95 @@
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, HTTPException, Request, Response
+
+from kf_oj.api.dependencies import (
+    SESSION_COOKIE,
+    current_principal,
+    identity_service,
+    trusted_origin,
+    unsafe_principal,
+)
+from kf_oj.contracts.identity import CurrentUser, LoginRequest, LoginResponse
+from kf_oj.modules.identity.public import AuthenticationFailed, LoginThrottled, Principal
+from kf_oj.modules.identity.service import IdentityService
+
+router = APIRouter(prefix="/auth", tags=["identity"])
+
+
+@router.post("/login", response_model=LoginResponse, dependencies=[Depends(trusted_origin)])
+async def login(
+    body: LoginRequest,
+    request: Request,
+    response: Response,
+    identity: Annotated[IdentityService, Depends(identity_service)],
+) -> LoginResponse:
+    if request.headers.get("content-type", "").split(";", 1)[0] != "application/json":
+        raise HTTPException(415, "JSON request required")
+    try:
+        issued = await identity.login(
+            body.username,
+            body.password.get_secret_value(),
+            peer=request.client.host if request.client else "",
+        )
+    except LoginThrottled:
+        raise HTTPException(
+            429, "login temporarily limited", headers={"Retry-After": "900"}
+        ) from None
+    except (AuthenticationFailed, ValueError):
+        raise HTTPException(401, "invalid credentials") from None
+    settings = request.app.state.settings
+    response.set_cookie(
+        SESSION_COOKIE,
+        issued.token,
+        max_age=settings.session_lifetime_seconds,
+        httponly=True,
+        secure=settings.environment == "production",
+        samesite="strict",
+        path="/api/v1",
+    )
+    response.set_cookie(
+        "kf_csrf",
+        issued.csrf_token,
+        max_age=settings.session_lifetime_seconds,
+        httponly=False,
+        secure=settings.environment == "production",
+        samesite="strict",
+        path="/",
+    )
+    response.headers["Cache-Control"] = "no-store"
+    return LoginResponse(
+        user=CurrentUser(id=issued.principal.account_id, username=issued.principal.username),
+        expires_at=issued.expires_at,
+        csrf_token=issued.csrf_token,
+    )
+
+
+@router.get("/me", response_model=CurrentUser)
+async def me(response: Response, principal: Annotated[Principal, Depends(current_principal)]):
+    response.headers["Cache-Control"] = "no-store"
+    return CurrentUser(id=principal.account_id, username=principal.username)
+
+
+@router.post("/logout", status_code=204, dependencies=[Depends(unsafe_principal)])
+async def logout(
+    request: Request, identity: Annotated[IdentityService, Depends(identity_service)]
+) -> Response:
+    try:
+        await identity.logout(request.cookies[SESSION_COOKIE], request.headers["x-csrf-token"])
+    except AuthenticationFailed:
+        raise HTTPException(401, "authentication required") from None
+    response = Response(status_code=204, headers={"Cache-Control": "no-store"})
+    response.delete_cookie(
+        SESSION_COOKIE,
+        path="/api/v1",
+        httponly=True,
+        secure=request.app.state.settings.environment == "production",
+        samesite="strict",
+    )
+    response.delete_cookie(
+        "kf_csrf",
+        path="/",
+        secure=request.app.state.settings.environment == "production",
+        samesite="strict",
+    )
+    return response
diff --git a/backend/src/kf_oj/contracts/identity.py b/backend/src/kf_oj/contracts/identity.py
new file mode 100644
index 0000000..c9a23a9
--- /dev/null
+++ b/backend/src/kf_oj/contracts/identity.py
@@ -0,0 +1,22 @@
+from datetime import datetime
+from typing import Annotated
+
+from pydantic import Field, SecretStr
+
+from kf_oj.contracts.judging import Digest, Identifier, WireModel
+
+
+class LoginRequest(WireModel):
+    username: Annotated[str, Field(strict=True, pattern=r"^[a-z0-9_]{3,24}$")]
+    password: Annotated[SecretStr, Field(min_length=12, max_length=128)]
+
+
+class CurrentUser(WireModel):
+    id: Identifier
+    username: str
+
+
+class LoginResponse(WireModel):
+    user: CurrentUser
+    expires_at: datetime
+    csrf_token: Digest = Field(repr=False)
diff --git a/backend/src/kf_oj/core/settings.py b/backend/src/kf_oj/core/settings.py
index f5fb278..2e29df1 100644
--- a/backend/src/kf_oj/core/settings.py
+++ b/backend/src/kf_oj/core/settings.py
@@ -1,6 +1,6 @@
 from typing import Literal
 
-from pydantic import SecretStr
+from pydantic import Field, SecretStr, model_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
 
@@ -11,3 +11,28 @@ class Settings(BaseSettings):
     log_level: Literal["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"] = "INFO"
     database_url: SecretStr | None = None
     amqp_url: SecretStr | None = None
+    browser_origins: tuple[str, ...] = ("http://localhost:5173", "http://localhost:8000")
+    session_lifetime_seconds: int = Field(default=43200, ge=300, le=86400)
+
+    @model_validator(mode="after")
+    def secure_origins(self):
+        from urllib.parse import urlsplit
+
+        if not self.browser_origins or len(self.browser_origins) > 8:
+            raise ValueError("one to eight browser origins required")
+        for origin in self.browser_origins:
+            parts = urlsplit(origin)
+            if (
+                parts.scheme not in {"http", "https"}
+                or not parts.hostname
+                or parts.username
+                or parts.password
+                or parts.path
+                or parts.query
+                or parts.fragment
+                or (self.environment == "production" and parts.scheme != "https")
+            ):
+                raise ValueError(
+                    "browser origins must be explicit origins; production requires HTTPS"
+                )
+        return self
diff --git a/backend/src/kf_oj/infra/db/session.py b/backend/src/kf_oj/infra/db/session.py
index 02806dd..ade3488 100644
--- a/backend/src/kf_oj/infra/db/session.py
+++ b/backend/src/kf_oj/infra/db/session.py
@@ -6,7 +6,21 @@ from kf_oj.core.settings import Settings
 def build_engine(settings: Settings) -> AsyncEngine:
     if settings.database_url is None:
         raise ValueError("KF_OJ_DATABASE_URL is required for database-backed operations")
-    return create_async_engine(settings.database_url.get_secret_value(), pool_pre_ping=True)
+    return create_async_engine(
+        settings.database_url.get_secret_value(),
+        pool_pre_ping=True,
+        pool_size=5,
+        max_overflow=0,
+        pool_timeout=5,
+        connect_args={
+            "command_timeout": 10,
+            "server_settings": {
+                "statement_timeout": "10000",
+                "lock_timeout": "5000",
+                "idle_in_transaction_session_timeout": "30000",
+            },
+        },
+    )
 
 
 def build_session_factory(engine: AsyncEngine) -> async_sessionmaker:
diff --git a/backend/src/kf_oj/modules/identity/README.md b/backend/src/kf_oj/modules/identity/README.md
index 299e021..c2b5e7e 100644
--- a/backend/src/kf_oj/modules/identity/README.md
+++ b/backend/src/kf_oj/modules/identity/README.md
@@ -1,5 +1,24 @@
 # identity
 
 负责账号、登录凭证、会话与角色；向其他模块提供经过验证的用户身份和授权依据。
-后续 `public.py` 暴露身份查询接口，`service.py` 编排用例，`repository.py` 封装持久化。
-用户身份不能来自前端自报字段或模型参数。目前仅建立模块边界，未实现登录。
+`public.py` 提供已验证主体，`service.py` 管理账号和可撤销会话，`repository.py` 封装持久化。
+用户身份不能来自前端自报字段或模型参数。
+
+本地管理命令为 `uv run --locked kf-accounts create <username>` / `disable <username>`。
+创建口令由隐藏终端提示读取和确认，不接受命令行参数、环境中的默认口令或自助注册。
+用户名为 3–24 个小写 ASCII 字母、数字或下划线；口令 12–128 字符，最多 512 UTF-8 字节。
+密码摘要由新增的 `argon2-cffi` 依赖提供 Argon2id，固定 19 MiB/2 次/1 并行度。
+参数依据 [OWASP](https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html)
+和 [argon2-cffi 文档](https://argon2-cffi.readthedocs.io/en/stable/parameters.html)。
+
+登录接口为 `/api/v1/auth/login`，退出 `/logout`，当前主体 `/me`。会话使用随机 256-bit token，
+数据库只保存 token / CSRF 摘要；默认 12 小时有效，单账号保留至多 10 个有效会话。
+账号禁用立即拒绝登录和旧会话。请求只采用实际连接 peer，不信任客户端自报身份或转发地址。
+每 peer 至多 10 次登录/15 分钟，预算通过真实数据库串行更新，失败尝试也消耗预算。
+摘要计算最多同时 2 次，超出直接 429；限流表至多 4096 桶且每次有界回收过期桶。
+
+有副作用的浏览器请求必须匹配 `KF_OJ_BROWSER_ORIGINS` 的显式来源；生产只接受 HTTPS 来源，
+必须提供生产来源配置。会话 Cookie 为 HttpOnly / SameSite=Strict，生产 Secure；CSRF Cookie
+供前端读出请求 token，在 `X-CSRF-Token` 携带，服务端核对其与当前会话绑定的摘要。
+登录、主体和退出响应不缓存；请求校验错误不回显密码或输入值。API 层限制请求字节、块数和
+读取期限。跨服务 Worker 凭证不使用用户 Cookie。
diff --git a/backend/src/kf_oj/modules/identity/cli.py b/backend/src/kf_oj/modules/identity/cli.py
new file mode 100644
index 0000000..56625f4
--- /dev/null
+++ b/backend/src/kf_oj/modules/identity/cli.py
@@ -0,0 +1,49 @@
+"""Controlled local account management; passwords are read from the terminal only."""
+
+import argparse
+import asyncio
+import getpass
+
+from sqlalchemy.exc import IntegrityError
+
+from kf_oj.core.settings import Settings
+from kf_oj.infra.db.session import build_engine, build_session_factory
+from kf_oj.modules.identity.service import IdentityService
+
+
+async def run(command: str, username: str, password: str | None = None) -> None:
+    engine = build_engine(Settings())
+    try:
+        service = IdentityService(build_session_factory(engine))
+        if command == "create":
+            assert password is not None
+            await service.create_account(username, password)
+            print("Account created.")
+        else:
+            if not await service.disable_account(username):
+                raise ValueError("account not found")
+            print("Account disabled; sessions revoked.")
+    finally:
+        await engine.dispose()
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="Manage local OJ accounts")
+    parser.add_argument("command", choices=("create", "disable"))
+    parser.add_argument("username")
+    args = parser.parse_args()
+    password = None
+    if args.command == "create":
+        password = getpass.getpass("Password (12–128 characters): ")
+        if password != getpass.getpass("Repeat password: "):
+            parser.error("passwords differ")
+    try:
+        asyncio.run(run(args.command, args.username, password))
+    except IntegrityError:
+        parser.exit(1, "Account operation rejected by database constraints.\n")
+    except ValueError as error:
+        parser.exit(1, f"Account operation rejected: {error}.\n")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/backend/src/kf_oj/modules/identity/passwords.py b/backend/src/kf_oj/modules/identity/passwords.py
new file mode 100644
index 0000000..f46aede
--- /dev/null
+++ b/backend/src/kf_oj/modules/identity/passwords.py
@@ -0,0 +1,32 @@
+"""Argon2id password verification with explicit bounded parameters."""
+
+import re
+
+from argon2 import PasswordHasher, Type
+from argon2.exceptions import InvalidHashError, VerificationError
+
+USERNAME = re.compile(r"[a-z0-9_]{3,24}\Z")
+HASHER = PasswordHasher(time_cost=2, memory_cost=19456, parallelism=1, type=Type.ID)
+
+
+def validate_account(username: str, password: str) -> None:
+    if not USERNAME.fullmatch(username) or not 12 <= len(password) <= 128:
+        raise ValueError("username or password outside account policy")
+    if len(password.encode("utf-8")) > 512:
+        raise ValueError("password outside byte policy")
+
+
+def hash_password(username: str, password: str) -> str:
+    validate_account(username, password)
+    return HASHER.hash(password)
+
+
+def verify_password(stored: str, password: str) -> bool:
+    try:
+        # Stored hashes are owner-controlled, but don't allow corrupted parameters to allocate
+        # arbitrary memory. Account creation always uses these exact parameters.
+        if not stored.startswith("$argon2id$v=19$m=19456,t=2,p=1$"):
+            return False
+        return HASHER.verify(stored, password)
+    except (VerificationError, InvalidHashError):
+        return False
diff --git a/backend/src/kf_oj/modules/identity/public.py b/backend/src/kf_oj/modules/identity/public.py
new file mode 100644
index 0000000..8e7b1ed
--- /dev/null
+++ b/backend/src/kf_oj/modules/identity/public.py
@@ -0,0 +1,18 @@
+"""Only verified principals cross business module boundaries."""
+
+from dataclasses import dataclass
+from uuid import UUID
+
+
+@dataclass(frozen=True)
+class Principal:
+    account_id: UUID
+    username: str
+
+
+class AuthenticationFailed(ValueError):
+    pass
+
+
+class LoginThrottled(ValueError):
+    pass
diff --git a/backend/src/kf_oj/modules/identity/repository.py b/backend/src/kf_oj/modules/identity/repository.py
new file mode 100644
index 0000000..a0470ff
--- /dev/null
+++ b/backend/src/kf_oj/modules/identity/repository.py
@@ -0,0 +1,85 @@
+from datetime import datetime
+
+from sqlalchemy import delete, func, select, text, update
+from sqlalchemy.dialects.postgresql import insert
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from kf_oj.modules.identity.models import Account, LoginThrottle, Session
+from kf_oj.modules.identity.public import LoginThrottled
+
+
+async def consume_login_budget(
+    session: AsyncSession, bucket: str, now: datetime, reset_at: datetime
+) -> None:
+    # An upsert establishes the key before FOR UPDATE; requests share one DB-backed budget.
+    inserted = await session.scalar(
+        insert(LoginThrottle)
+        .values(bucket_hash=bucket, attempts=1, reset_at=reset_at)
+        .on_conflict_do_nothing(index_elements=[LoginThrottle.bucket_hash])
+        .returning(LoginThrottle.bucket_hash)
+    )
+    row = await session.scalar(
+        select(LoginThrottle).where(LoginThrottle.bucket_hash == bucket).with_for_update()
+    )
+    assert row is not None
+    # The initial upsert consumes this request only if there was no prior row.
+    # A separate returning flag avoids granting an extra request during concurrency.
+    if inserted is not None:
+        return
+    if row.reset_at <= now:
+        row.attempts, row.reset_at = 1, reset_at
+    elif row.attempts >= 10:
+        raise LoginThrottled("login request budget exhausted")
+    else:
+        row.attempts += 1
+
+
+async def prune_throttles(session: AsyncSession, now: datetime, *, limit: int = 100) -> None:
+    await session.execute(text("SELECT pg_advisory_xact_lock(-740164777)"))
+    keys = select(LoginThrottle.bucket_hash).where(LoginThrottle.reset_at <= now)
+    keys = keys.order_by(LoginThrottle.reset_at).limit(limit).with_for_update(skip_locked=True)
+    await session.execute(delete(LoginThrottle).where(LoginThrottle.bucket_hash.in_(keys)))
+
+
+async def check_throttle_capacity(session: AsyncSession, bucket: str) -> None:
+    if await session.get(LoginThrottle, bucket) is None:
+        if await session.scalar(select(func.count()).select_from(LoginThrottle)) >= 4096:
+            raise LoginThrottled("login throttle capacity exhausted")
+
+
+async def account_by_username(session: AsyncSession, username: str) -> Account | None:
+    return await session.scalar(select(Account).where(Account.username == username))
+
+
+async def current_session(session: AsyncSession, token_hash: str):
+    return (
+        await session.execute(
+            select(Session, Account)
+            .join(Account)
+            .where(
+                Session.token_hash == token_hash,
+                Session.revoked_at.is_(None),
+                Session.expires_at > func.now(),
+                Account.enabled.is_(True),
+            )
+        )
+    ).one_or_none()
+
+
+async def prune_sessions(session: AsyncSession, account_id) -> None:
+    await session.execute(
+        delete(Session).where(
+            Session.account_id == account_id,
+            (Session.expires_at <= func.now()) | Session.revoked_at.is_not(None),
+        )
+    )
+    # Keep at most nine older valid sessions before adding the new one.
+    old = select(Session.token_hash).where(Session.account_id == account_id)
+    old = old.order_by(Session.created_at.desc(), Session.token_hash).offset(9)
+    await session.execute(delete(Session).where(Session.token_hash.in_(old)))
+
+
+async def revoke(session: AsyncSession, token_hash: str) -> None:
+    await session.execute(
+        update(Session).where(Session.token_hash == token_hash).values(revoked_at=func.now())
+    )
diff --git a/backend/src/kf_oj/modules/identity/service.py b/backend/src/kf_oj/modules/identity/service.py
new file mode 100644
index 0000000..e8cb3af
--- /dev/null
+++ b/backend/src/kf_oj/modules/identity/service.py
@@ -0,0 +1,131 @@
+import asyncio
+import hashlib
+import hmac
+import re
+import secrets
+from dataclasses import dataclass, field
+from datetime import datetime, timedelta
+from uuid import uuid4
+
+from sqlalchemy import func, select, update
+from sqlalchemy.ext.asyncio import async_sessionmaker
+
+from kf_oj.modules.identity import repository
+from kf_oj.modules.identity.models import Account, Session
+from kf_oj.modules.identity.passwords import (
+    HASHER,
+    hash_password,
+    validate_account,
+    verify_password,
+)
+from kf_oj.modules.identity.public import AuthenticationFailed, LoginThrottled, Principal
+
+TOKEN = re.compile(r"[0-9a-f]{64}\Z")
+
+
+def token_digest(value: str) -> str:
+    return hashlib.sha256(value.encode("ascii")).hexdigest()
+
+
+@dataclass(frozen=True)
+class IssuedSession:
+    principal: Principal
+    expires_at: datetime
+    token: str = field(repr=False)
+    csrf_token: str = field(repr=False)
+
+
+class IdentityService:
+    def __init__(self, sessions: async_sessionmaker, *, lifetime_seconds: int = 43200):
+        if not 300 <= lifetime_seconds <= 86400:
+            raise ValueError("invalid session lifetime")
+        self.sessions = sessions
+        self.lifetime_seconds = lifetime_seconds
+        self._hash_slots = asyncio.Semaphore(2)
+        self._dummy_hash = HASHER.hash(secrets.token_hex(32))
+
+    async def create_account(self, username: str, password: str) -> Principal:
+        hashed = await asyncio.to_thread(hash_password, username, password)
+        async with self.sessions.begin() as session:
+            account = Account(id=uuid4(), username=username, password_hash=hashed)
+            session.add(account)
+        return Principal(account.id, username)
+
+    async def disable_account(self, username: str) -> bool:
+        async with self.sessions.begin() as session:
+            account = await repository.account_by_username(session, username)
+            if account is None:
+                return False
+            account.enabled = False
+            await session.execute(
+                update(Session)
+                .where(Session.account_id == account.id)
+                .values(revoked_at=func.now())
+            )
+            return True
+
+    async def login(self, username: str, password: str, *, peer: str) -> IssuedSession:
+        validate_account(username, password)
+        if not peer or len(peer) > 128:
+            raise AuthenticationFailed("invalid login context")
+        # Fail fast instead of allowing an unbounded password-hash queue.
+        if self._hash_slots.locked():
+            raise LoginThrottled("password verification capacity exhausted")
+        async with self._hash_slots:
+            async with self.sessions.begin() as session:
+                now = await session.scalar(select(func.now()))
+                assert now is not None
+                await repository.prune_throttles(session, now)
+                # Direct peer only; caller must never substitute forwarded client headers.
+                bucket = hashlib.sha256(peer.encode("utf-8")).hexdigest()
+                await repository.check_throttle_capacity(session, bucket)
+                await repository.consume_login_budget(
+                    session, bucket, now, now + timedelta(minutes=15)
+                )
+            async with self.sessions() as session:
+                account = await repository.account_by_username(session, username)
+                hashed = account.password_hash if account is not None else self._dummy_hash
+            correct = await asyncio.to_thread(verify_password, hashed, password)
+            if not correct or account is None or not account.enabled:
+                raise AuthenticationFailed("invalid credentials")
+            token, csrf = secrets.token_hex(32), secrets.token_hex(32)
+            async with self.sessions.begin() as session:
+                # Serialize with disabling the account and concurrent logins before issuing.
+                account = await session.scalar(
+                    select(Account).where(Account.id == account.id).with_for_update()
+                )
+                if account is None or not account.enabled:
+                    raise AuthenticationFailed("invalid credentials")
+                now = await session.scalar(select(func.now()))
+                expires = now + timedelta(seconds=self.lifetime_seconds)
+                await repository.prune_sessions(session, account.id)
+                session.add(
+                    Session(
+                        token_hash=token_digest(token),
+                        account_id=account.id,
+                        csrf_hash=token_digest(csrf),
+                        expires_at=expires,
+                    )
+                )
+                principal = Principal(account.id, account.username)
+            return IssuedSession(principal, expires, token, csrf)
+
+    async def authenticate(self, token: str | None, *, csrf_token: str | None = None) -> Principal:
+        if token is None or not TOKEN.fullmatch(token):
+            raise AuthenticationFailed("invalid session")
+        async with self.sessions() as session:
+            row = await repository.current_session(session, token_digest(token))
+            if row is None:
+                raise AuthenticationFailed("invalid session")
+            record, account = row
+            if csrf_token is not None:
+                if not TOKEN.fullmatch(csrf_token) or not hmac.compare_digest(
+                    record.csrf_hash, token_digest(csrf_token)
+                ):
+                    raise AuthenticationFailed("invalid request token")
+            return Principal(account.id, account.username)
+
+    async def logout(self, token: str, csrf_token: str) -> None:
+        await self.authenticate(token, csrf_token=csrf_token)
+        async with self.sessions.begin() as session:
+            await repository.revoke(session, token_digest(token))
diff --git a/backend/tests/test_health.py b/backend/tests/test_health.py
index 76a1d16..00e7424 100644
--- a/backend/tests/test_health.py
+++ b/backend/tests/test_health.py
@@ -21,7 +21,9 @@ def test_liveness_without_database_or_queue() -> None:
 
 
 def test_production_disables_api_documentation() -> None:
-    app = create_app(Settings(_env_file=None, environment="production"))
+    app = create_app(
+        Settings(_env_file=None, environment="production", browser_origins=("https://oj.example",))
+    )
 
     async def request():
         async with httpx.AsyncClient(
diff --git a/backend/tests/test_identity.py b/backend/tests/test_identity.py
new file mode 100644
index 0000000..42de122
--- /dev/null
+++ b/backend/tests/test_identity.py
@@ -0,0 +1,284 @@
+import asyncio
+import os
+import pty
+import secrets
+import select as io_select
+import signal
+import sys
+import time
+from datetime import timedelta
+from uuid import uuid4
+
+import httpx
+import pytest
+from sqlalchemy import event, func, select, update
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+
+from kf_oj.api.app import create_app
+from kf_oj.contracts.identity import LoginRequest
+from kf_oj.core.settings import Settings
+from kf_oj.modules.identity.models import Account, Session
+from kf_oj.modules.identity.passwords import hash_password, verify_password
+from kf_oj.modules.identity.public import AuthenticationFailed, LoginThrottled
+from kf_oj.modules.identity.service import IdentityService, token_digest
+
+
+def restrict_platform_role(engine):
+    @event.listens_for(engine.sync_engine, "connect")
+    def apply_role(connection, _):
+        cursor = connection.cursor()
+        cursor.execute("SET ROLE kf_oj_platform")
+        cursor.close()
+
+
+def test_password_policy_and_credentials_redacted():
+    password = secrets.token_hex(16)
+    hashed = hash_password("fixture_user", password)
+    assert hashed.startswith("$argon2id$v=19$m=19456,t=2,p=1$")
+    assert verify_password(hashed, password)
+    assert not verify_password(hashed, secrets.token_hex(16))
+    assert not verify_password("$argon2id$v=19$m=999999999,t=2,p=1$invalid", password)
+    assert password not in repr(LoginRequest(username="fixture_user", password=password))
+    with pytest.raises(ValueError):
+        hash_password("not canonical", password)
+    with pytest.raises(ValueError):
+        hash_password("fixture_user", "too short")
+
+
+def test_production_cookie_configuration_requires_explicit_https_origins():
+    with pytest.raises(ValueError):
+        Settings(_env_file=None, environment="production")
+    for invalid in ("https://oj.example/path", "https://user@oj.example", "*", "null"):
+        with pytest.raises(ValueError):
+            Settings(_env_file=None, browser_origins=(invalid,))
+
+
+def test_real_login_session_revocation_expiry_and_throttle(postgres_url):
+    async def run():
+        engine = create_async_engine(postgres_url)
+        restrict_platform_role(engine)
+        sessions = async_sessionmaker(engine, expire_on_commit=False)
+        identity = IdentityService(sessions, lifetime_seconds=300)
+        password = secrets.token_hex(16)
+        try:
+            principal = await identity.create_account("fixture_user", password)
+            with pytest.raises(AuthenticationFailed):
+                await identity.login("fixture_user", secrets.token_hex(16), peer="fixture-peer")
+            with pytest.raises(AuthenticationFailed):
+                await identity.login("absent_user", password, peer="fixture-peer")
+            issued = await identity.login("fixture_user", password, peer="fixture-peer")
+            assert await identity.authenticate(issued.token) == principal
+            assert issued.token not in repr(issued) and issued.csrf_token not in repr(issued)
+            with pytest.raises(AuthenticationFailed):
+                await identity.authenticate(str(principal.account_id))
+            with pytest.raises(AuthenticationFailed):
+                await identity.authenticate(issued.token, csrf_token="f" * 64)
+            await identity.logout(issued.token, issued.csrf_token)
+            with pytest.raises(AuthenticationFailed):
+                await identity.authenticate(issued.token)
+            issued = await identity.login("fixture_user", password, peer="expiry-peer")
+            async with sessions.begin() as session:
+                # Keep the expiry constraint valid while moving the entire session into the past.
+                await session.execute(
+                    update(Session).values(
+                        created_at=func.now() - timedelta(minutes=10),
+                        expires_at=func.now() - timedelta(minutes=5),
+                    )
+                )
+            with pytest.raises(AuthenticationFailed):
+                await identity.authenticate(issued.token)
+            issued = await identity.login("fixture_user", password, peer="disable-peer")
+            assert await identity.disable_account("fixture_user")
+            with pytest.raises(AuthenticationFailed):
+                await identity.authenticate(issued.token)
+            with pytest.raises(AuthenticationFailed):
+                await identity.login("fixture_user", password, peer="disable-peer")
+            assert not await identity.disable_account("unknown_user")
+            # Exactly ten real failed attempts consume the same persistent peer budget.
+            for _ in range(10):
+                with pytest.raises(AuthenticationFailed):
+                    await identity.login("absent_user", password, peer="limited-peer")
+            with pytest.raises(LoginThrottled):
+                await identity.login("absent_user", password, peer="limited-peer")
+            async with sessions() as session:
+                account = await session.scalar(select(Account))
+                assert password != account.password_hash and password not in account.password_hash
+                rows = list(await session.scalars(select(Session)))
+                assert all(row.token_hash != issued.token for row in rows)
+        finally:
+            await engine.dispose()
+
+    asyncio.run(run())
+
+
+def test_real_http_cookie_csrf_and_identity_spoofing_rejection(postgres_url, caplog):
+    async def run():
+        app = create_app(
+            Settings(
+                _env_file=None,
+                environment="production",
+                database_url=postgres_url,
+                browser_origins=("https://test",),
+            )
+        )
+        async with app.router.lifespan_context(app):
+            restrict_platform_role(app.state.sessions.kw["bind"])
+            password = secrets.token_hex(16)
+            first = await app.state.identity.create_account("first_user", password)
+            second = await app.state.identity.create_account("second_user", secrets.token_hex(16))
+            headers = {"Origin": "https://test"}
+            async with httpx.AsyncClient(
+                transport=httpx.ASGITransport(app=app), base_url="https://test"
+            ) as client:
+                body = {"username": "first_user", "password": password}
+                assert (await client.get("/api/v1/auth/me")).status_code == 401
+                assert (await client.post("/api/v1/auth/login", json=body)).status_code == 403
+                assert (
+                    await client.post(
+                        "/api/v1/auth/login",
+                        json=body,
+                        headers={"Origin": "https://hostile.example"},
+                    )
+                ).status_code == 403
+                invalid = await client.post(
+                    "/api/v1/auth/login",
+                    headers=headers,
+                    json=body | {"user_id": str(second.account_id), "role": "admin"},
+                )
+                assert invalid.status_code == 422
+                assert password not in invalid.text and "admin" not in invalid.text
+                response = await client.post("/api/v1/auth/login", json=body, headers=headers)
+                assert response.status_code == 200
+                assert response.json()["user"]["id"] == str(first.account_id)
+                assert (
+                    await client.get(
+                        "/api/v1/auth/me", headers={"X-User-ID": str(second.account_id)}
+                    )
+                ).json()["id"] == str(first.account_id)
+                cookie = response.headers.get_list("set-cookie")[0]
+                assert "HttpOnly" in cookie and "Secure" in cookie and "SameSite=strict" in cookie
+                assert response.headers["cache-control"] == "no-store"
+                assert client.cookies.get("kf_csrf") == response.json()["csrf_token"]
+                assert (
+                    await client.post("/api/v1/auth/logout", headers=headers)
+                ).status_code == 403
+                assert (
+                    await client.post(
+                        "/api/v1/auth/logout", headers=headers | {"X-CSRF-Token": "f" * 64}
+                    )
+                ).status_code == 403
+                assert (
+                    await client.post(
+                        "/api/v1/auth/logout",
+                        headers=headers | {"X-CSRF-Token": response.json()["csrf_token"]},
+                    )
+                ).status_code == 204
+                assert (await client.get("/api/v1/auth/me")).status_code == 401
+                assert not client.cookies.get("kf_session") and not client.cookies.get("kf_csrf")
+                assert (
+                    password not in caplog.text and response.json()["csrf_token"] not in caplog.text
+                )
+
+    asyncio.run(run())
+
+
+def test_real_concurrent_logins_keep_bounded_active_sessions(postgres_url):
+    async def run():
+        engine = create_async_engine(postgres_url)
+        restrict_platform_role(engine)
+        sessions = async_sessionmaker(engine, expire_on_commit=False)
+        identity = IdentityService(sessions)
+        password = secrets.token_hex(16)
+        try:
+            await identity.create_account("fixture_user", password)
+            # Independent peer budgets exercise session bounds without exhausting login retries.
+            issued = []
+            for _ in range(12):
+                issued.append(await identity.login("fixture_user", password, peer=uuid4().hex))
+            with pytest.raises(AuthenticationFailed):
+                await identity.authenticate(issued[0].token)
+            results = await asyncio.gather(
+                *(identity.login("fixture_user", password, peer=uuid4().hex) for _ in range(3)),
+                return_exceptions=True,
+            )
+            assert sum(isinstance(result, LoginThrottled) for result in results) == 1
+            assert sum(not isinstance(result, Exception) for result in results) == 2
+            async with sessions() as session:
+                assert await session.scalar(select(func.count()).select_from(Session)) == 10
+                assert (
+                    await session.scalar(
+                        select(func.count())
+                        .select_from(Session)
+                        .where(Session.token_hash == token_digest("0" * 64))
+                    )
+                    == 0
+                )
+        finally:
+            await engine.dispose()
+
+    asyncio.run(run())
+
+
+def test_account_cli_hidden_password_and_disable(postgres_url):
+    password = secrets.token_hex(16)
+    # The CLI prompts through a real private PTY; the password is never an argument/environment.
+    pid, descriptor = pty.fork()
+    if pid == 0:
+        os.environ["KF_OJ_DATABASE_URL"] = postgres_url
+        os.execv(
+            sys.executable,
+            [sys.executable, "-m", "kf_oj.modules.identity.cli", "create", "cli_user"],
+        )
+    output = b""
+    deadline, prompts, status = time.monotonic() + 15, 0, None
+    try:
+        while time.monotonic() < deadline:
+            if io_select.select([descriptor], [], [], 0.1)[0]:
+                try:
+                    block = os.read(descriptor, 4096)
+                except OSError:
+                    block = b""
+                output += block
+                if prompts == 0 and b"Password (12" in output:
+                    os.write(descriptor, password.encode() + b"\n")
+                    prompts = 1
+                if prompts == 1 and b"Repeat password:" in output:
+                    os.write(descriptor, password.encode() + b"\n")
+                    prompts = 2
+            result, status = os.waitpid(pid, os.WNOHANG)
+            if result:
+                break
+        else:
+            os.kill(pid, signal.SIGTERM)
+            os.waitpid(pid, 0)
+            pytest.fail("account CLI deadline exceeded")
+        assert os.waitstatus_to_exitcode(status) == 0
+        assert prompts == 2 and b"Account created." in output
+        assert password.encode() not in output
+    finally:
+        os.close(descriptor)
+
+    async def inspect():
+        engine = create_async_engine(postgres_url)
+        sessions = async_sessionmaker(engine, expire_on_commit=False)
+        try:
+            service = IdentityService(sessions)
+            issued = await service.login("cli_user", password, peer="cli-fixture")
+            from kf_oj.modules.identity.cli import run
+
+            await run("disable", "cli_user")
+            with pytest.raises(AuthenticationFailed):
+                await service.authenticate(issued.token)
+        finally:
+            await engine.dispose()
+
+    # CLI run uses the test DB only for this call; don't reuse a configured business database.
+    original = os.environ.get("KF_OJ_DATABASE_URL")
+    os.environ["KF_OJ_DATABASE_URL"] = postgres_url
+    try:
+        asyncio.run(inspect())
+    finally:
+        if original is None:
+            os.environ.pop("KF_OJ_DATABASE_URL", None)
+        else:
+            os.environ["KF_OJ_DATABASE_URL"] = original
diff --git a/backend/uv.lock b/backend/uv.lock
index 34143de..7c004ba 100644
--- a/backend/uv.lock
+++ b/backend/uv.lock
@@ -73,6 +73,40 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/12/b8/4bd346e22b28902df4d651910f5242c28d84e4a5c2435ca5c3f797ed7e2e/anyio-4.15.1-py3-none-any.whl", hash = "sha256:6152fdbbf9a77fdec97731721bebf7c4c44f7c29b424b0065826173efc7ed101", size = 132079, upload-time = "2026-09-05T10:42:37.923Z" },
 ]
 
+[[package]]
+name = "argon2-cffi"
+version = "25.1.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "argon2-cffi-bindings" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/0e/89/ce5af8a7d472a67cc819d5d998aa8c82c5d860608c4db9f46f1162d7dab9/argon2_cffi-25.1.0.tar.gz", hash = "sha256:694ae5cc8a42f4c4e2bf2ca0e64e51e23a040c6a517a85074683d3959e1346c1", size = 45706, upload-time = "2025-06-03T06:55:32.073Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/4f/d3/a8b22fa575b297cd6e3e3b0155c7e25db170edf1c74783d6a31a2490b8d9/argon2_cffi-25.1.0-py3-none-any.whl", hash = "sha256:fdc8b074db390fccb6eb4a3604ae7231f219aa669a2652e0f20e16ba513d5741", size = 14657, upload-time = "2025-06-03T06:55:30.804Z" },
+]
+
+[[package]]
+name = "argon2-cffi-bindings"
+version = "26.1.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "cffi" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/0b/43/bb8b6e8708d49a5ab36781333af092d9f483b198a2710d01281204640055/argon2_cffi_bindings-26.1.0.tar.gz", hash = "sha256:63505c71542a44b68b1e38060450fb006404170da375feb31af153e7f9c6205d", size = 1790807, upload-time = "2026-08-20T07:44:22.492Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/e7/d2/0ae991f1b2181e5be49007c574710a800ad36c2978683addb3e67c474e55/argon2_cffi_bindings-26.1.0-cp310-abi3-macosx_11_0_arm64.whl", hash = "sha256:21ca0396fe5ec995dd54431c32698189666f9224810acfa752e50d2bd94d9df2", size = 25521, upload-time = "2026-08-20T07:32:43.019Z" },
+    { url = "https://files.pythonhosted.org/packages/7e/e4/ad91d8297638aa2258aad4501c306aca99480dfe76ccd638173fa3702db9/argon2_cffi_bindings-26.1.0-cp310-abi3-manylinux_2_26_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:78de2d65e0b9ea7ce9d1b1c3e87297b2d7305a02c266ee2a2d6910daddd7ee69", size = 27177, upload-time = "2026-08-20T07:32:44.158Z" },
+    { url = "https://files.pythonhosted.org/packages/6f/86/5363df11b86d02cf3662208e7406496327649cc90eb365bf6f4e8a54a41f/argon2_cffi_bindings-26.1.0-cp310-abi3-manylinux_2_26_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:27f1821903e2ceadcb88ec2b45ef190897b7682449c772f4d9b53e42c520cf29", size = 26597, upload-time = "2026-08-20T07:32:45.172Z" },
+    { url = "https://files.pythonhosted.org/packages/f4/b5/a14dcc592652347dad23ee93b278a4da5d2a25c9ed3ebd10d68eea823a4f/argon2_cffi_bindings-26.1.0-cp310-abi3-manylinux_2_34_riscv64.manylinux_2_39_riscv64.whl", hash = "sha256:d88e5f7e60f28ae0b0cc6b2f16c43e87cd642a196a86f85e0d8bb6fe016fc16d", size = 27403, upload-time = "2026-08-20T07:32:46.13Z" },
+    { url = "https://files.pythonhosted.org/packages/b3/81/b4a20d4902af7f796390bf9245ff83c5217dfa7367efa1d14986956c482b/argon2_cffi_bindings-26.1.0-cp310-abi3-musllinux_1_2_aarch64.whl", hash = "sha256:34b7d9c24a4165a2c61cc8ae11d44d48c9ce2830fb536cb7914e11fdd9962728", size = 27132, upload-time = "2026-08-20T07:32:47.13Z" },
+    { url = "https://files.pythonhosted.org/packages/7e/1b/c8de358af07b1c490e0fcb863ef98e46ddb486e45567aca5a60bd68d9daa/argon2_cffi_bindings-26.1.0-cp310-abi3-musllinux_1_2_riscv64.whl", hash = "sha256:224865cbbcb7a2bd1356741dff12b0134df726b6d44bb7b500df8e303cbd9e81", size = 27588, upload-time = "2026-08-20T07:32:48.087Z" },
+    { url = "https://files.pythonhosted.org/packages/48/2f/7ee62a6e79f9309f9d9982d301b22a00010adb580c05c8109b94d7b33de0/argon2_cffi_bindings-26.1.0-cp310-abi3-musllinux_1_2_x86_64.whl", hash = "sha256:ffff613aaa9ce6236766e2fc6dc560bb5abde7a2e2416e3db1f9ae395a2b4dd4", size = 26785, upload-time = "2026-08-20T07:32:48.977Z" },
+    { url = "https://files.pythonhosted.org/packages/e9/10/960d0ee93d4897741bcaf4799c697dae2d81499f66fd1ed042a7dd54c1f4/argon2_cffi_bindings-26.1.0-cp310-abi3-win32.whl", hash = "sha256:a86c069c91a747a2c4e5c51473590aeb48172fff9b2130d23729a42d98665ecb", size = 23898, upload-time = "2026-08-20T07:32:50.114Z" },
+    { url = "https://files.pythonhosted.org/packages/6d/3a/0cc14a05810e6add9bce5e87693334baa2222de5f647fa31781885b6573f/argon2_cffi_bindings-26.1.0-cp310-abi3-win_amd64.whl", hash = "sha256:2c36ff87b5dfaa477d0bd51e9d7f6abdae7c8955d2983c97419085d842154b3e", size = 25730, upload-time = "2026-08-20T07:32:51.091Z" },
+    { url = "https://files.pythonhosted.org/packages/4e/db/d83cf2af140547f0b9cdaece05b2dc2dcbf991be4667331d073eff771435/argon2_cffi_bindings-26.1.0-cp310-abi3-win_arm64.whl", hash = "sha256:f9c4420a7a864fe1b86ce35befc95b8e39fb852493b81cf798671ddc265de638", size = 24478, upload-time = "2026-08-20T07:32:52.111Z" },
+    { url = "https://files.pythonhosted.org/packages/bb/5f/f652055e18d2627e2eed94c7f31a792127cfe38df786635395d742321674/argon2_cffi_bindings-26.1.0-cp313-cp313-pyemscripten_2025_0_wasm32.whl", hash = "sha256:af11ac37a7c53dc16cb7950a6190851b0870fe218b6c60c0bb7ac355234e3083", size = 15434, upload-time = "2026-08-20T07:32:53.143Z" },
+]
+
 [[package]]
 name = "asyncpg"
 version = "0.31.0"
@@ -107,6 +141,31 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/0b/a7/71ac2cff56fec219ed242bb11b8efb69fcc4bec75db06fb7bfe35de520e6/certifi-2026.7.22-py3-none-any.whl", hash = "sha256:62f22742b58a1a33014a2b6b706588a8d7e2a88ae7bd1a6ebe8c992928483775", size = 136983, upload-time = "2026-07-22T03:35:11.276Z" },
 ]
 
+[[package]]
+name = "cffi"
+version = "2.1.1"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "pycparser", marker = "implementation_name != 'PyPy'" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/9e/ef/008a1939e372c06329a3fce4279c02f328488f3526744906eeec3da7ad5f/cffi-2.1.1.tar.gz", hash = "sha256:dd31f52ea1086513bb9df30f8fcee9b8918323ae067a3d5b78bc826a000712be", size = 530807, upload-time = "2026-08-03T21:21:18.939Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/9d/f4/035513d4117049066b4779dc3b7c0c0fdad175fa13731c9f4003f1cd1478/cffi-2.1.1-cp313-cp313-ios_13_0_arm64_iphoneos.whl", hash = "sha256:b5bdfd1c873d4e093aabc0ca84c4ca6dbc4f752afb5c86f146d9742580c9da2e", size = 194248, upload-time = "2026-08-03T21:19:59.399Z" },
+    { url = "https://files.pythonhosted.org/packages/76/af/2aeb4dbb5fc41a04161ae9ff1518de7cec08e164f44a8ce6a4cf7fd2cd1d/cffi-2.1.1-cp313-cp313-ios_13_0_arm64_iphonesimulator.whl", hash = "sha256:31348097ff5bbe827ccc41795d4dd099d9f0625e7def00ee653c137a490c2a6c", size = 196908, upload-time = "2026-08-03T21:20:00.746Z" },
+    { url = "https://files.pythonhosted.org/packages/a7/46/2e5fdde8555706dd98139a910ca11be02809f3f605ce956f655d0214e100/cffi-2.1.1-cp313-cp313-macosx_10_15_x86_64.whl", hash = "sha256:9d2055050ea716bd38b7f7f1579c275386646b4894c155a3e2f3cd62ed41b7c6", size = 184805, upload-time = "2026-08-03T21:20:02.02Z" },
+    { url = "https://files.pythonhosted.org/packages/55/41/4c7042f317b9217502988f0873af87e16ad606dc20f84e546e3e6ce9764c/cffi-2.1.1-cp313-cp313-macosx_11_0_arm64.whl", hash = "sha256:19ee6127ee34de7d83ce3d371ebc5ed91addbdcc39f9ab15ce4eb35a4e534971", size = 184764, upload-time = "2026-08-03T21:20:03.141Z" },
+    { url = "https://files.pythonhosted.org/packages/43/1f/1c3d90d91811c8f86ced9ed637956c54bfe5b79ca98fe976d7f8c8979f6b/cffi-2.1.1-cp313-cp313-manylinux1_i686.manylinux2014_i686.manylinux_2_17_i686.manylinux_2_5_i686.whl", hash = "sha256:6a8dddef476fab96d066d578fc88526767b836ab5ab21754e1d5bf3879c31c7c", size = 214722, upload-time = "2026-08-03T21:20:04.377Z" },
+    { url = "https://files.pythonhosted.org/packages/37/6f/3b5ce4c3b2192d250f04908f2bfd91ef34552ec8f7716a5d4abdb8d67bb2/cffi-2.1.1-cp313-cp313-manylinux2014_aarch64.manylinux_2_17_aarch64.whl", hash = "sha256:f16c709686a78c727bbbf059f92b0bf41c6fc60deec706d2dc19f529175a6125", size = 222369, upload-time = "2026-08-03T21:20:05.544Z" },
+    { url = "https://files.pythonhosted.org/packages/02/10/4b3c75dde3d9663c9e02ba05c2668b954f671d4bbe346413ca8c696b295a/cffi-2.1.1-cp313-cp313-manylinux2014_ppc64le.manylinux_2_17_ppc64le.whl", hash = "sha256:fcd22650c908d7b7da162bbfaab594a1227a15d1643a98c68b122ac642fa2264", size = 210175, upload-time = "2026-08-03T21:20:06.75Z" },
+    { url = "https://files.pythonhosted.org/packages/df/62/14f74b9543e605d17701dc797b815958b8bb70b7624ce1b832ddad48ed6c/cffi-2.1.1-cp313-cp313-manylinux2014_s390x.manylinux_2_17_s390x.whl", hash = "sha256:aa9511c62d14da7aacc9b4bf51f3f697a621e83b2d6919008243c3aad168eea3", size = 208670, upload-time = "2026-08-03T21:20:08.04Z" },
+    { url = "https://files.pythonhosted.org/packages/95/95/86342356ff5953b3fb06f7ef7c5bee212d45e770abc7218d451b9148313c/cffi-2.1.1-cp313-cp313-manylinux2014_x86_64.manylinux_2_17_x86_64.whl", hash = "sha256:a931079504ecc49efed7744c476a5c343a92fabf66dec2db95edb1b2fdc770e2", size = 221824, upload-time = "2026-08-03T21:20:09.274Z" },
+    { url = "https://files.pythonhosted.org/packages/eb/ff/7b3429ff53aafe931ed8a5fc69f481bbef7ba6de87ddcbb63d08f483f613/cffi-2.1.1-cp313-cp313-musllinux_1_2_aarch64.whl", hash = "sha256:a2d7755bef5a12ed488f4ef1f1b69ee9191d7396083b755a5d2295f6edb4768b", size = 225148, upload-time = "2026-08-03T21:20:10.7Z" },
+    { url = "https://files.pythonhosted.org/packages/34/34/a95870b9221e09cf4f2ce3178b1a210abdfe63a1bd357da940418d7b8d15/cffi-2.1.1-cp313-cp313-musllinux_1_2_x86_64.whl", hash = "sha256:e0bcb7e0f677f543555d2adff3bf19c05f66cdb4796e5ff602442ab2fe3c4ef7", size = 223564, upload-time = "2026-08-03T21:20:12.165Z" },
+    { url = "https://files.pythonhosted.org/packages/70/ea/839b50531021a647fb5e929f72cf97bc1ff702b5472166164b5b6e76b851/cffi-2.1.1-cp313-cp313-win32.whl", hash = "sha256:334644fbac4eff73d985a17a91226df55d0f394160c4cfb880e084c8f7161cac", size = 175263, upload-time = "2026-08-03T21:20:13.559Z" },
+    { url = "https://files.pythonhosted.org/packages/60/a6/8b149b2c3f2e11aaa1618ef64500b45f50f22c57a977a4dff1aff1f91042/cffi-2.1.1-cp313-cp313-win_amd64.whl", hash = "sha256:1aa5645c30469b09530c4ebca77ebf8f17618293c58f8549cb1a543a50236e7d", size = 185688, upload-time = "2026-08-03T21:20:14.69Z" },
+    { url = "https://files.pythonhosted.org/packages/01/9a/11f687cb39d6a3504060d5242f04f48c735afb4d3d533958a20594890cb2/cffi-2.1.1-cp313-cp313-win_arm64.whl", hash = "sha256:63bbfd5ded17c4840ac07cd8f1c21ba9d9708141f840b324f422f41b207e3973", size = 180078, upload-time = "2026-08-03T21:20:15.917Z" },
+]
+
 [[package]]
 name = "click"
 version = "8.5.0"
@@ -249,6 +308,7 @@ source = { editable = "." }
 dependencies = [
     { name = "aio-pika" },
     { name = "alembic" },
+    { name = "argon2-cffi" },
     { name = "asyncpg" },
     { name = "fastapi" },
     { name = "pydantic" },
@@ -269,6 +329,7 @@ dev = [
 requires-dist = [
     { name = "aio-pika", specifier = ">=9.5,<10" },
     { name = "alembic", specifier = ">=1.15,<2" },
+    { name = "argon2-cffi", specifier = ">=25.1,<26" },
     { name = "asyncpg", specifier = ">=0.30,<1" },
     { name = "fastapi", specifier = ">=0.115,<1" },
     { name = "pydantic", specifier = ">=2.10,<3" },
@@ -422,6 +483,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/f5/cd/785c64ed382f3f04201870267b02783f63b4678c2acfddc177a3ebcc2727/propcache-0.5.4-py3-none-any.whl", hash = "sha256:62c60aec739ed00124573cce1178138fd690c7676352d67a37328c1cf51d7468", size = 16338, upload-time = "2026-09-16T00:17:13.106Z" },
 ]
 
+[[package]]
+name = "pycparser"
+version = "3.1"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/ac/d3/eb1d3bc30dda12f7e69640ae2ac8cb10240b71fb73024ad528b7d2ae73da/pycparser-3.1.tar.gz", hash = "sha256:b3fc6dec06a8b2fefa0ed4ff92285306a5e3be9987bc5603c9edbdc4e492418f", size = 105946, upload-time = "2026-10-08T12:26:34.349Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/99/ce/b3ae9ee0324d991c860187be2a6ee436d27a3d02397eaddbb101ec901f3d/pycparser-3.1-py3-none-any.whl", hash = "sha256:f09d358c840bd147b79e55f2bc494f18ea869dc897f5852a8f5766b74f787882", size = 48709, upload-time = "2026-10-08T12:26:32.97Z" },
+]
+
 [[package]]
 name = "pydantic"
 version = "2.13.5"
diff --git a/contracts/openapi/platform.v1.json b/contracts/openapi/platform.v1.json
index 4401d71..4040e32 100644
--- a/contracts/openapi/platform.v1.json
+++ b/contracts/openapi/platform.v1.json
@@ -1,6 +1,39 @@
 {
   "components": {
     "schemas": {
+      "CurrentUser": {
+        "additionalProperties": false,
+        "properties": {
+          "id": {
+            "format": "uuid",
+            "title": "Id",
+            "type": "string"
+          },
+          "username": {
+            "title": "Username",
+            "type": "string"
+          }
+        },
+        "required": [
+          "id",
+          "username"
+        ],
+        "title": "CurrentUser",
+        "type": "object"
+      },
+      "HTTPValidationError": {
+        "properties": {
+          "detail": {
+            "items": {
+              "$ref": "#/components/schemas/ValidationError"
+            },
+            "title": "Detail",
+            "type": "array"
+          }
+        },
+        "title": "HTTPValidationError",
+        "type": "object"
+      },
       "HealthResponse": {
         "additionalProperties": false,
         "properties": {
@@ -26,16 +59,183 @@
         ],
         "title": "HealthResponse",
         "type": "object"
+      },
+      "LoginRequest": {
+        "additionalProperties": false,
+        "properties": {
+          "password": {
+            "format": "password",
+            "maxLength": 128,
+            "minLength": 12,
+            "title": "Password",
+            "type": "string",
+            "writeOnly": true
+          },
+          "username": {
+            "pattern": "^[a-z0-9_]{3,24}$",
+            "title": "Username",
+            "type": "string"
+          }
+        },
+        "required": [
+          "username",
+          "password"
+        ],
+        "title": "LoginRequest",
+        "type": "object"
+      },
+      "LoginResponse": {
+        "additionalProperties": false,
+        "properties": {
+          "csrf_token": {
+            "maxLength": 64,
+            "minLength": 64,
+            "pattern": "^[0-9a-f]{64}$",
+            "title": "Csrf Token",
+            "type": "string"
+          },
+          "expires_at": {
+            "format": "date-time",
+            "title": "Expires At",
+            "type": "string"
+          },
+          "user": {
+            "$ref": "#/components/schemas/CurrentUser"
+          }
+        },
+        "required": [
+          "user",
+          "expires_at",
+          "csrf_token"
+        ],
+        "title": "LoginResponse",
+        "type": "object"
+      },
+      "ValidationError": {
+        "properties": {
+          "ctx": {
+            "title": "Context",
+            "type": "object"
+          },
+          "input": {
+            "title": "Input"
+          },
+          "loc": {
+            "items": {
+              "anyOf": [
+                {
+                  "type": "string"
+                },
+                {
+                  "type": "integer"
+                }
+              ]
+            },
+            "title": "Location",
+            "type": "array"
+          },
+          "msg": {
+            "title": "Message",
+            "type": "string"
+          },
+          "type": {
+            "title": "Error Type",
+            "type": "string"
+          }
+        },
+        "required": [
+          "loc",
+          "msg",
+          "type"
+        ],
+        "title": "ValidationError",
+        "type": "object"
       }
     }
   },
   "info": {
-    "description": "工程骨架。当前只提供进程存活检查，业务接口逐项实现。",
+    "description": "平台 API。身份使用真实可撤销会话，业务接口按模块逐项接入。",
     "title": "KF-OnlineJudge Platform API",
     "version": "0.0.1"
   },
   "openapi": "3.1.0",
   "paths": {
+    "/api/v1/auth/login": {
+      "post": {
+        "operationId": "login_api_v1_auth_login_post",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/LoginRequest"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "200": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/LoginResponse"
+                }
+              }
+            },
+            "description": "Successful Response"
+          },
+          "422": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/HTTPValidationError"
+                }
+              }
+            },
+            "description": "Validation Error"
+          }
+        },
+        "summary": "Login",
+        "tags": [
+          "identity"
+        ]
+      }
+    },
+    "/api/v1/auth/logout": {
+      "post": {
+        "operationId": "logout_api_v1_auth_logout_post",
+        "responses": {
+          "204": {
+            "description": "Successful Response"
+          }
+        },
+        "summary": "Logout",
+        "tags": [
+          "identity"
+        ]
+      }
+    },
+    "/api/v1/auth/me": {
+      "get": {
+        "operationId": "me_api_v1_auth_me_get",
+        "responses": {
+          "200": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/CurrentUser"
+                }
+              }
+            },
+            "description": "Successful Response"
+          }
+        },
+        "summary": "Me",
+        "tags": [
+          "identity"
+        ]
+      }
+    },
     "/api/v1/health/live": {
       "get": {
         "description": "Check process liveness only; does not attest DB, queue or judge readiness.",
diff --git a/frontend/src/api/generated/schema.d.ts b/frontend/src/api/generated/schema.d.ts
index 1872ce9..2d40995 100644
--- a/frontend/src/api/generated/schema.d.ts
+++ b/frontend/src/api/generated/schema.d.ts
@@ -4,6 +4,57 @@
  */
 
 export interface paths {
+    "/api/v1/auth/login": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get?: never;
+        put?: never;
+        /** Login */
+        post: operations["login_api_v1_auth_login_post"];
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
+    "/api/v1/auth/logout": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get?: never;
+        put?: never;
+        /** Logout */
+        post: operations["logout_api_v1_auth_logout_post"];
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
+    "/api/v1/auth/me": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        /** Me */
+        get: operations["me_api_v1_auth_me_get"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/api/v1/health/live": {
         parameters: {
             query?: never;
@@ -28,6 +79,21 @@ export interface paths {
 export type webhooks = Record<string, never>;
 export interface components {
     schemas: {
+        /** CurrentUser */
+        CurrentUser: {
+            /**
+             * Id
+             * Format: uuid
+             */
+            id: string;
+            /** Username */
+            username: string;
+        };
+        /** HTTPValidationError */
+        HTTPValidationError: {
+            /** Detail */
+            detail?: components["schemas"]["ValidationError"][];
+        };
         /** HealthResponse */
         HealthResponse: {
             /**
@@ -43,6 +109,40 @@ export interface components {
             /** Version */
             version: string;
         };
+        /** LoginRequest */
+        LoginRequest: {
+            /**
+             * Password
+             * Format: password
+             */
+            password: string;
+            /** Username */
+            username: string;
+        };
+        /** LoginResponse */
+        LoginResponse: {
+            /** Csrf Token */
+            csrf_token: string;
+            /**
+             * Expires At
+             * Format: date-time
+             */
+            expires_at: string;
+            user: components["schemas"]["CurrentUser"];
+        };
+        /** ValidationError */
+        ValidationError: {
+            /** Context */
+            ctx?: Record<string, never>;
+            /** Input */
+            input?: unknown;
+            /** Location */
+            loc: (string | number)[];
+            /** Message */
+            msg: string;
+            /** Error Type */
+            type: string;
+        };
     };
     responses: never;
     parameters: never;
@@ -52,6 +152,77 @@ export interface components {
 }
 export type $defs = Record<string, never>;
 export interface operations {
+    login_api_v1_auth_login_post: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody: {
+            content: {
+                "application/json": components["schemas"]["LoginRequest"];
+            };
+        };
+        responses: {
+            /** @description Successful Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["LoginResponse"];
+                };
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
+    logout_api_v1_auth_logout_post: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Successful Response */
+            204: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+        };
+    };
+    me_api_v1_auth_me_get: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Successful Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["CurrentUser"];
+                };
+            };
+        };
+    };
     liveness: {
         parameters: {
             query?: never;