Mock client credentials machine auth in Python

import time
import hashlib
import secrets

class MachineAuth:
    """Mock client-credentials machine auth for service-to-service calls."""
    
    def __init__(self, client_id, client_secret):
        self.client_id = client_id
        self.client_secret = client_secret
        self._token = None
        self._expires_at = 0
    
    def authenticate(self):
        """Return a mock bearer token, caching it if still valid."""
        now = time.time()
        if self._token and now < self._expires_at:
            return self._token
        
        # Simulate OAuth2 client-credentials exchange
        raw = f"{self.client_id}:{self.client_secret}:{int(now)}"
        self._token = hashlib.sha256(raw.encode()).hexdigest()
        self._expires_at = now + 3600
        return self._token
    
    def get_auth_header(self):
        token = self.authenticate()
        return {"Authorization": f"Bearer {token}"}

    def revoke(self):
        """Simulate token revocation."""
        self._token = None
        self._expires_at = 0

if __name__ == "__main__":
    auth = MachineAuth("service-a", "supersecret")
    print("Header:", auth.get_auth_header())
    print("Cached token:", auth.authenticate() == auth.authenticate())
    auth.revoke()
    print("After revoke, regen:", auth.get_auth_header() != auth.get_auth_header())