"Invalid token" in keycloak

I am trying to use keycloak in my FastAPI app My code

from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import jwt, JWTError
from keycloak import KeycloakOpenID
import requests
import logging
import os

from .config import settings


# Configure logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

# Keycloak configuration
KEYCLOAK_SERVER_URL = settings.KEYCLOAK_SERVER_URL
KEYCLOAK_REALM = settings.KEYCLOAK_REALM
KEYCLOAK_CLIENT_ID = settings.KEYCLOAK_CLIENT_ID
KEYCLOAK_CLIENT_SECRET = settings.KEYCLOAK_CLIENT_SECRET
ALGORITHM = "RS256"
TOKEN_URL = f"{KEYCLOAK_SERVER_URL}/realms/fastapi-realm/protocol/openid-connect/token"


# Initialize KeycloakOpenID
keycloak_openid = KeycloakOpenID(
    server_url=f"{KEYCLOAK_SERVER_URL}",
    client_id=KEYCLOAK_CLIENT_ID,
    realm_name=KEYCLOAK_REALM,
    client_secret_key=KEYCLOAK_CLIENT_SECRET,
    verify=False
)
config_well_known = keycloak_openid.well_known()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def verify_token(token: str = Depends(oauth2_scheme)):
    try:
        decoded_token = keycloak_openid.decode_token(
            token,validate=True,
        )
        username = decoded_token['preferred_username']
        logger.info(f"Decoded token: {decoded_token}")
        # Verify the issuer claim
        issuer = decoded_token["iss"]

        expected_issuer = f"{KEYCLOAK_SERVER_URL}/realms/{KEYCLOAK_REALM}"
        I# Token example -- token: {'exp': 1731303036, 'iat': 1731267036, 'jti': 'f1b71d25-4de6-4c03-b5f5-d9726b39d51f', 'iss': 'https://feast-keycloak.pimc-st.innodev.local/realms/feast-realm', 'aud': 'account', 'sub': 'ac48f45e-f26b-4380-bde8-e752febb6d18', 'typ': 'Bearer', 'azp': 'feast-client-id', 'session_state': 'b36cd197-247d-447e-9f3d-6cf1fecae7d6', 'acr': '1', 'allowed-origins': ['https://feast-frontend.pimc-st.innodev.local', '/*', 'http://localhost:5173'], 'realm_access': {'roles': ['default-roles-feast-realm', 'offline_access', 'uma_authorization']}, 'resource_access': {'account': {'roles': ['manage-account', 'manage-account-links', 'view-profile']}}, 'scope': 'profile email', 'sid': 'b36cd197-247d-447e-9f3d-6cf1fecae7d6', 'email_verified': False, 'name': 'A B', 'preferred_username': 'my_username', 'given_name': 'A', 'family_name': 'B', 'email': 'aamoskalenko@inno.tech'}
        logger.info(f"XXX_ issuer={issuer}")
        logger.info(f"XXX_ expected_issuer={expected_issuer}")
        if issuer != expected_issuer:
            raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid issuer")
        
        logger.info(f"username: {username}")
        return decoded_token
    except Exception as e:
        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED, detail="Invalid token")

In my main.py I have the following code

from fastapi import Depends, FastAPI, HTTPException, status, Security


from .keycloak import verify_token, oauth2_scheme, KEYCLOAK_CLIENT_ID, KEYCLOAK_CLIENT_SECRET, TOKEN_URL

app = FastAPI()

@app.post("/project", response_model=schemas.Project, tags=["project",])
def create_project(project: schemas.CreateProject, db: Session = Depends(get_db), payload: dict = Security(verify_token)):
    ...


@app.post("/login")
def get_token(body: schemas.Login):
    data = {
        "grant_type": "password", # TODO: clarify grant_type client_credentials (requires only client id and secret or password - requires password and login)
        "client_id": KEYCLOAK_CLIENT_ID,
        "client_secret": KEYCLOAK_CLIENT_SECRET,
        "password": body.password,
        "username": body.login
    }
    response = requests.post(TOKEN_URL, data=data,  verify=False)
    return JSONResponse(status_code=response.status_code, content=response.json())

I am obtaining token with help of /login method Then I am applying token like this:

For requet /project I have an error:

"Invalid token"

How to fix the error?

This 3 Steps can verify token

Step 1: Fetch the public key certificate from Keycloak to verify the JWT token signature.

Step 2: Convert the certificate into a usable public key format.

Step 3: Decode and verify the JWT token signature using the public key, while skipping audience and issuer checks.

    # Step 1: Get public key for signature verification
    certs_url = f"{self.keycloak_url}/realms/{self.realm}/protocol/openid-connect/certs"
    certs_response = requests.get(certs_url)
    certs_response.raise_for_status()
    public_key_data = certs_response.json()
    certificate_pem = f"-----BEGIN CERTIFICATE-----\n{public_key_data['keys'][0]['x5c'][0]}\n-----END CERTIFICATE-----"

    # Step 2: Convert certificate to public key
    cert = x509.load_pem_x509_certificate(certificate_pem.encode('utf-8'), default_backend())
    public_key = cert.public_key().public_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PublicFormat.SubjectPublicKeyInfo
    )

    # Step 3: Use jwt.decode only for signature verification, disabling audience and issuer checks
    jwt.decode(
        token,
        public_key,
        algorithms=['RS256'],
        options={
            'verify_aud': False,
            'verify_iss': False
        }
    )

Launching Key cloak by Docker Compose

version: '3.8'

services:
  postgres:
    image: postgres:15.6
    container_name: postgres_db
    restart: always
    ports:
      - "5432:5432"
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      POSTGRES_DB: keycloak
      POSTGRES_USER: keycloak
      POSTGRES_PASSWORD: password

  keycloak_web:
    image: quay.io/keycloak/keycloak:26.0.5
    container_name: keycloak_web
    environment:
      KC_DB: postgres
      KC_DB_URL: jdbc:postgresql://postgres:5432/keycloak
      KC_DB_USERNAME: keycloak
      KC_DB_PASSWORD: password

      KC_HOSTNAME: localhost
      KC_HOSTNAME_STRICT: false
      KC_HOSTNAME_STRICT_HTTPS: false

      KC_LOG_LEVEL: info
      KC_METRICS_ENABLED: true
      KC_HEALTH_ENABLED: true
      KEYCLOAK_ADMIN: admin
      KEYCLOAK_ADMIN_PASSWORD: admin
    command: start-dev
    depends_on:
      - postgres
    ports:
      - 8080:8080

volumes:
  postgres_data:

Create realm & user

realm

fastapi-realm

user

username: user1
password: 1234

Install dependency in Python 3.12 with conda

pip install fastapi uvicorn requests python-keycloak python-jose cryptography

FastAPI server code

api-server.py

from fastapi import FastAPI, HTTPException, Depends
from pydantic import BaseModel
from starlette.responses import JSONResponse
from keycloak import KeycloakOpenID
from jose import jwt, JWTError
from cryptography import x509
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization

import requests
import json

app = FastAPI()

# Configuration variables
KEYCLOAK_URL = 'http://localhost:8080'
REALM = 'fastapi-realm'
TOKEN_URL = f"{KEYCLOAK_URL}/realms/{REALM}/protocol/openid-connect/token"
KEYCLOAK_CLIENT_ID = 'admin-cli'

# Keycloak service class
class KeycloakService:
    def __init__(self):
        self.keycloak_url = KEYCLOAK_URL
        self.realm = REALM

    def decode_and_print_token(self, token):
        try:
            # Retrieve claims without verifying the signature or audience
            decoded_token = jwt.get_unverified_claims(token)
            print("Decoded JWT token:")
            print(json.dumps(decoded_token, indent=4))
            return decoded_token
        except JWTError as e:
            print(f"Error decoding token: {e}")
            return None
        
    def validate_token(self, token: str, client_id: str) -> bool:
        decoded_token = self.decode_and_print_token(token)
        if not decoded_token:
            print("Failed to decode token.")
            return False

        try:
            # Extract issuer, azp, and aud directly from decoded token
            issuer = decoded_token.get('iss')
            authorized_party = decoded_token.get('azp')
            audience = decoded_token.get('aud')

            print("Issuer (iss) in token:", issuer)
            print("Authorized party (azp) in token:", authorized_party)
            print("Audience (aud) in token:", audience)

            expected_issuer = f"{self.keycloak_url}/realms/{self.realm}"
            if issuer != expected_issuer:
                print(f"Invalid issuer. Expected: {expected_issuer}, Got: {issuer}")
                return False

            # Allow `aud` to be `None` for user tokens, or match "account" or the client_id for client tokens
            if audience is None:
                print("Audience is None, assuming this is a user token without an audience.")
            elif audience not in ["account", client_id]:
                print(f"Invalid audience. Expected: 'account' or '{client_id}', Got: {audience}")
                return False

            # Step 1: Get public key for signature verification
            certs_url = f"{self.keycloak_url}/realms/{self.realm}/protocol/openid-connect/certs"
            certs_response = requests.get(certs_url)
            certs_response.raise_for_status()
            public_key_data = certs_response.json()
            certificate_pem = f"-----BEGIN CERTIFICATE-----\n{public_key_data['keys'][0]['x5c'][0]}\n-----END CERTIFICATE-----"

            # Step 2: Convert certificate to public key
            cert = x509.load_pem_x509_certificate(certificate_pem.encode('utf-8'), default_backend())
            public_key = cert.public_key().public_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PublicFormat.SubjectPublicKeyInfo
            )

            # Step 3: Use jwt.decode only for signature verification, disabling audience and issuer checks
            jwt.decode(
                token,
                public_key,
                algorithms=['RS256'],
                options={
                    'verify_aud': False,
                    'verify_iss': False
                }
            )
            print("Token signature is valid.")
            return True
        except JWTError as e:
            print(f"Error validating token: {e}")
            return False
        except requests.RequestException as e:
            print(f"Error fetching public key: {e}")
            return False

keycloak_service = KeycloakService()

# Schemas
class Login(BaseModel):
    login: str
    password: str

class VerifyToken(BaseModel):
    token: str
    client_id: str

# Login endpoint
@app.post("/login")
def get_token(body: Login):
    data = {
        "grant_type": "password",
        "client_id": KEYCLOAK_CLIENT_ID,
        "username": body.login,
        "password": body.password
    }
    response = requests.post(TOKEN_URL, data=data, verify=False)
    if response.status_code == 200:
        return JSONResponse(status_code=200, content=response.json())
    else:
        raise HTTPException(status_code=response.status_code, detail=response.json())

# Verify endpoint
@app.post("/verify")
def verify_token(body: VerifyToken):
    is_valid = keycloak_service.validate_token(body.token, body.client_id)
    return {"valid": is_valid}

Launching FastAPI server

uvicorn api-server:app --reload

API document URL

http://localhost:8000/docs#/

Get Token by Postman

URL

POST http://localhost:8000/login

Input Body

{
  "login": "user1",
  "password": "1234"
}

Script for assign user_token variable

var jsonData = JSON.parse(responseBody);

if (jsonData.access_token) {
    postman.setEnvironmentVariable("user_token", jsonData.access_token);
} else {
    console.error("access_token not found in the response");
}

Verify Token by Postman

URL

POST http://localhost:8000/verify

Input Body

{
  "token": "{{user_token}}",
  "client_id": "admin-cli"
}

So the user token verified with OK (true) value.

Token Valid Result

{
    "valid": true
}