Call init from auth managers only once

[vincbeck]

The method init from auth managers is called multiples times for two reasons:

• The method init is also called in the Flask applications. This is only needed for fab auth manager. Thus, I created a method specific init_flask_resources in FAB auth manager that I call in the Flask applications
• fastapi spins up multiple workers (4 by default), therefore init is called 4 times. I updated the init function of simple auth manager to be called only once

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[bugraoz93]

Looks cool!

[Copilot]

Pull Request Overview

This PR ensures that the auth manager initialization is only executed once per process, addressing the multiple invocations caused by the Flask application and FastAPI’s multi-worker environment. Key changes include:

• Adding file locking in SimpleAuthManager to restrict the init method to a single execution.
• Updating and adding tests to verify the correct handling of passwords and file content.
• Modifying FAB auth manager to use a dedicated method (init_flask_resources) for initialization in Flask applications.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/api_fastapi/auth/managers/simple/test_simple_auth_manager.py	Added tests covering password file reading/updating and filtering of user entries.
airflow/api_fastapi/auth/managers/simple/simple_auth_manager.py	Introduced file locking via fcntl in the init method and refactored password retrieval logic.
providers/fab/src/airflow/providers/fab/www/extensions/init_appbuilder.py	Modified to call init_flask_resources instead of init for FAB auth manager.
providers/fab/src/airflow/providers/fab/auth_manager/fab_auth_manager.py	Renamed init to init_flask_resources, aligning with the new initialization strategy.

Comments suppressed due to low confidence (1)

airflow/api_fastapi/auth/managers/simple/simple_auth_manager.py:127

• Typo in the comment: 'User dot not exist in the file' should be corrected to 'User does not exist in the file'.

# User dot not exist in the file, adding it