Support client_credentials grant type

README.md

@@ -35,17 +35,38 @@ MULTIPASS_IDENTITY_PROVIDERS = {
         'title': 'Keycloak Identity Provider',
         'identifier_field': 'email',
         'keycloak_args': {
-            'client_name': '<client_name>',
+            'grant_type': 'client_credentials',
+            'client_id': '<client_id>',
             'client_secret': '<client_secret>',
-            'username': <username>,
-            'password': <password>,
-            'access_token_url': <access-token-url>,
-            'realm_api_url': <realm-api-url>
+            'access_token_url': '<access-token-url>',
+            'realm_api_url': '<realm-api-url>'
         }
     }
 }
 ```
 
+The configuration values are following:
+
+1. `grant_type`
+
+   Default value is `client_credentials`. In Keycloak, "Service accounts roles" must be enabled in client config (Client details/Settings/Capability).
+
+   `password` is also supported. In Keycloak, "Direct access grants" must be enabled in client config (Client details/Settings/Capability). In this case 2 additional fields must be added: `username` and `password`.
+
+2. `client_id`
+
+   In Keycloak, Client details/Setting/Client ID field.
+3. `client_secret`
+
+   In Keycloak, Client details/Credentials/Client Secret field.
+4. `access_token_url`
+
+   In Keycloak, Realm settings/General/Endpoints/OpenID Endpoint Configuration/"token_endpoint".
+5. `realm_api_url`
+
+   The URL format is `<base url>/admin/realms/<realm name>`, where the realm is where the users and user groups are configured.
+
+
 ### Performance
 
 The library needs to get an API access token from Keycloak which typically takes 200-300ms. Set the `cache` key of the multipass identity provider configuration to the import path of a Flask-Caching instance or a function returning such an instance, or the instance itself to enable caching of tokens (until they expire) and group data (30 minutes).

src/flask_multipass_keycloak.py

@@ -209,12 +209,16 @@ def _get_api_session(self):
         if api_token:
             api_session.headers.update({'Authorization': f'Bearer {api_token}'})
             return api_session
-        basic = HTTPBasicAuth(self.keycloak_settings['client_name'], self.keycloak_settings['client_secret'])
-        data = {'username': self.keycloak_settings['username'],
-                'password': self.keycloak_settings['password'],
-                'grant_type': 'password'}
+        data = {'client_id': self.keycloak_settings['client_id'],
+                'client_secret': self.keycloak_settings['client_secret'],
+                'grant_type': self.keycloak_settings['grant_type']}
+        # Supported grant types: password and client_credentials
+        if data['grant_type'] == 'password':
+            data |= {'username': self.keycloak_settings['username'],
+                     'password': self.keycloak_settings['password']}
+
         self.logger.info('Requesting access token')
-        response = api_session.post(self.keycloak_settings['access_token_url'], auth=basic, data=data)
+        response = api_session.post(self.keycloak_settings['access_token_url'], data=data)
         if response.status_code != 200:
             error_message = self._get_error_message(response)
             self.logger.error(f'{error_message} (URL: %s)', response.url)