tiangolo/fastapi · error · HTTPException

Incorrect username or password

Error message

Incorrect username or password

What it means

Default-parameter twin of error 51: `/token` raises HTTP 401 'Incorrect username or password' (with `WWW-Authenticate: Bearer`) when `authenticate_user` returns falsy. A `DUMMY_HASH` verify runs for unknown users to flatten timing differences. Behavior matches the Annotated version.

Source

Thrown at docs_src/security/tutorial004_py310.py:124

    user = get_user(fake_users_db, username=token_data.username)
    if user is None:
        raise credentials_exception
    return user


async def get_current_active_user(current_user: User = Depends(get_current_user)):
    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: OAuth2PasswordRequestForm = Depends(),
) -> Token:
    user = authenticate_user(fake_users_db, form_data.username, form_data.password)
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Bearer"},
        )
    access_token_expires = timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
    access_token = create_access_token(
        data={"sub": user.username}, 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: User = Depends(get_current_active_user)) -> User:
    return current_user


@app.get("/users/me/items/")
async def read_own_items(current_user: User = Depends(get_current_active_user)):

View on GitHub (pinned to 42a41db11f)

Solutions

1. POST credentials form-encoded.
2. Produce the stored hash with the same `PasswordHash.recommended()` the app uses.
3. Install `pwdlib[argon2]` if using argon2id.
4. Verify the username exists and the hash verifies.

Example fix

# before
# hash made by a different hasher => 401
# after
from pwdlib import PasswordHash
ph = PasswordHash.recommended()
db['johndoe']['hashed_password'] = ph.hash('secret')

def is_form_login(username: str, password: str) -> bool:
    return bool(username) and bool(password)
# POST as application/x-www-form-urlencoded when True

def is_credentials_error(resp) -> bool:
    return getattr(resp, 'status_code', None) == 401 and \
           resp.json().get('detail') == 'Incorrect username or password'

try:
    tok = client.post('/token', data={'username': u, 'password': p})
    tok.raise_for_status()
except httpx.HTTPStatusError as e:
    if e.response.status_code == 401 and 'Incorrect' in e.response.text:
        show_user_friendly_login_error()
    raise

When it happens

Trigger: `POST /token` with an unknown username or a known username + wrong password; both hit `if not user:` at line 123.

Common situations: Password typo; user not provisioned; argon2id hash mismatch from a different hasher; pwdlib missing/wrong version; JSON body instead of form data.

Related errors

• Incorrect username or password
• Incorrect username or password
• Incorrect username or password
• Incorrect username or password
• Incorrect username or password

AI-assisted analysis of tiangolo/fastapi@42a41db11f (2026-08-04). Data as JSON: /data/errors/9f7f33fb9d084c8a.json. Report an issue: GitHub.