tiangolo/fastapi · error · HTTPException

Incorrect username or password

Error message

Incorrect username or password

What it means

The /token handler in the scopes tutorial raises HTTP 400 'Incorrect username or password' when authenticate_user is falsy. Note the status inconsistency: tutorial005 uses 400 here whereas tutorial004 used 401 — both share the same authenticate_user (with DUMMY_HASH timing protection) and the same anti-enumeration message.

Solutions

1. POST username + password matching a seeded user (johndoe or alice with their original plaintext).
2. If you changed the hasher, regenerate the stored argon2 hashes with get_password_hash.
3. Standardize the status code on 401 with WWW-Authenticate for consistency with RFC 6749 and tutorial004.

Example fix

// before
if not user:
    raise HTTPException(status_code=400, detail="Incorrect username or password")

// after
if not user:
    raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Incorrect username or password", headers={"WWW-Authenticate": "Bearer"})

import httpx
def post_token(client: httpx.Client, u: str, p: str, scopes: str = ""):
    assert u and p, "username/password required"
    data = {"username": u, "password": p}
    if scopes:
        data["scope"] = scopes
    return client.post("/token", data=data)

from typing import TypeGuard
def is_valid_creds(pair: tuple) -> TypeGuard[tuple[str, str]]:
    u, p = pair
    return isinstance(u, str) and isinstance(p, str) and u.strip() and p

import httpx
try:
    r = httpx.post("/token", data={"username": u, "password": p, "scope": "me items"})
    r.raise_for_status()
except httpx.HTTPStatusError as e:
    if e.response.status_code in (400, 401):
        show_generic_login_error()

When it happens

Trigger: POST /token (form-encoded) with username not in {johndoe, alice} or a password that fails argon2 verification. The form may also carry a scope field, but a credential failure short-circuits before scopes matter.

Common situations: Wrong password; missing username field; regenerated argon2 hashes; sending JSON instead of form data.

Related errors

• Inactive user
• Inactive user
• Incorrect username or password
• Inactive user
• Incorrect username or password

AI-assisted analysis of tiangolo/fastapi@3e8d1526d8 (2026-08-11). Data as JSON: /api/errors/8b5d2ffd48e1d414. Report an issue: GitHub.

Appendix: source

Thrown at docs_src/security/tutorial005_an_py310.py:157

            )
    return user


async def get_current_active_user(
    current_user: Annotated[User, Security(get_current_user, scopes=["me"])],
):
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")
    return current_user


@app.post("/token")
async def login_for_access_token(
    form_data: Annotated[OAuth2PasswordRequestForm, Depends()],
) -> Token:
    user = authenticate_user(fake_users_db, form_data.username, form_data.password)
    if not user:
        raise HTTPException(status_code=400, detail="Incorrect username or password")
    access_token_expires = timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
    access_token = create_access_token(
        data={"sub": user.username, "scope": " ".join(form_data.scopes)},
        expires_delta=access_token_expires,
    )
    return Token(access_token=access_token, token_type="bearer")


@app.get("/users/me/")
async def read_users_me(
    current_user: Annotated[User, Depends(get_current_active_user)],
) -> User:
    return current_user


@app.get("/users/me/items/")
async def read_own_items(
    current_user: Annotated[User, Security(get_current_active_user, scopes=["items"])],

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