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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Illegal Firebase credential provided. App must be initialized with a valid credential instance error - when using another type of `google.auth.Credential` object with the SDK.","articleBody":"Hi there, I am having some issues using the `firebase_admin` python client with a credential object from outside the SDK.\r\n\r\nIn my use case, I want to initialize the `firebase_admin` SDK using a Service Account impersonation credential to list users within the firebase environment.\r\n\r\nTo do this I tried the following:\r\n\r\n```python\r\nimport google.oauth2.credentials\r\nimport google.auth.impersonated_credentials\r\n\r\nsource_credentials = google.oauth2.credentials.Credentials(token=id_token)\r\ncredentials = google.auth.impersonated_credentials.Credentials(\r\n    source_credentials=source_credentials,\r\n    target_principal=my_service_account_email,\r\n    target_scopes=target_scopes,\r\n    lifetime=500\r\n)\r\n\r\napp_options = {'projectId': project_id}\r\nfirebase_app = firebase_admin.initialize_app(\r\n  credential=firebase_credential, options=app_options)\r\n```\r\n\r\nWhen running `initialize_app` it returns an exception - `Illegal Firebase credential provided. App must be initialized with a valid credential instance`.\r\n\r\nLooking into the `firebase-admin-python` source code I was able to find the source of the problem. In `firebase_admin/__init__.py` line 209 the code checks whether the supplied `credentials` object is an instance of `firebase_admin.credentials.Base`. If not, then the SDK returns the exception.\r\n\r\nI don't understand why this is the case. Why does `firebase-admin-python` have its own credentials class which seems to just wrap `google.oauth2.credentials` objects? Why wouldn't the Firebase SDK accept a `google.oauth2.credentials` object directly?\r\n\r\nI was able to work around it by hacking the `ApplicationDefault` class that comes with the `firebase-admin-python` SDK, however this seems a bit backwards.\r\n\r\n```python\r\nfirebase_credential = firebase_admin.credentials.ApplicationDefault()\r\nfirebase_credential._g_credential = credentials\r\nfirebase_credential._project_id = SOURCE_PROJECT\r\n```\r\n\r\nIn my opinion it would be better if the firebase SDK just made use of the `google.auth` module which has a much better implementation.\r\n","author":{"url":"https://github.com/LPLabrys99","@type":"Person","name":"LPLabrys99"},"datePublished":"2023-05-04T15:35:32.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/698/firebase-admin-python/issues/698"}