Fix CORS issues and add Origin logging for debugging

[KnellBalm]

This PR addresses the reported CORS issue where the frontend (us-central1 region) was blocked from accessing the backend.

Changes:

1. Observability: Added LogOriginMiddleware to log the Origin header of incoming requests. This helps verify if the browser is sending the expected origin and if it matches the allowed list/regex in the production environment.
2. Configuration: Refactored backend/main.py to ensure cloud_origins and cloud_origin_regex are correctly defined and applied. The regex r"https://query-craft-frontend.*\.run\.app" supports various regional subdomains.
3. Middleware Order: Explicitly ordered middleware (LogOrigin -> CORS -> Exception -> PathRewrite) to ensure proper handling of headers and logging.

Tests:

• Verified locally with tests/reproduce_cors.py (created and then deleted).
• Ran existing tests tests/test_cors_config.py and tests/test_auth.py which passed.

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PR created automatically by Jules for task 1347566996273756232 started by @KnellBalm

Summary by Sourcery

Clarify and harden CORS configuration while adding request origin logging for improved CORS debugging and error observability.

Bug Fixes:

• Correct CORS configuration and middleware ordering to ensure Cloud Run frontend origins are properly allowed in production and development environments.

Enhancements:

• Centralize Cloud Run origin and regex definitions for reuse across environments.
• Introduce middleware to log incoming request Origin headers, paths, and methods before CORS handling for easier debugging of CORS issues.
• Standardize middleware logging by using a shared backend.middleware logger for exception and origin logging.

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[sourcery-ai]

Reviewer's Guide

Refactors CORS configuration in backend/main.py for clearer environment-specific setup, centralizes Cloud Run origin settings, and introduces a LogOriginMiddleware with explicit middleware ordering to aid CORS debugging and exception handling.

Sequence diagram for updated middleware order and CORS debugging

sequenceDiagram
    participant Client
    participant LogErrorsMiddleware
    participant LogOriginMiddleware
    participant CORSMiddleware
    participant ExceptionHandlingMiddleware
    participant PathRewriteMiddleware
    participant Router

    Client->>LogErrorsMiddleware: HTTP request
    LogErrorsMiddleware->>LogOriginMiddleware: request
    LogOriginMiddleware->>LogOriginMiddleware: Read Origin header
    LogOriginMiddleware->>LogOriginMiddleware: logger.info Origin, Path, Method
    LogOriginMiddleware->>CORSMiddleware: request
    CORSMiddleware->>ExceptionHandlingMiddleware: request
    ExceptionHandlingMiddleware->>PathRewriteMiddleware: request
    PathRewriteMiddleware->>Router: rewritten request
    Router-->>PathRewriteMiddleware: response
    PathRewriteMiddleware-->>ExceptionHandlingMiddleware: response
    ExceptionHandlingMiddleware-->>CORSMiddleware: response
    CORSMiddleware-->>LogOriginMiddleware: response with CORS headers
    LogOriginMiddleware-->>LogErrorsMiddleware: response
    LogErrorsMiddleware-->>Client: HTTP response

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Class diagram for updated middleware structure and logging

classDiagram
    class BaseHTTPMiddleware {
        <<framework>>
        +dispatch(request, call_next)
    }

    class PathRewriteMiddleware {
        +dispatch(request, call_next)
    }

    class ExceptionHandlingMiddleware {
        +dispatch(request, call_next)
    }

    class LogOriginMiddleware {
        +dispatch(request, call_next)
    }

    class Logger {
        <<logging>>
        +info(message)
        +error(message)
    }

    BaseHTTPMiddleware <|-- PathRewriteMiddleware
    BaseHTTPMiddleware <|-- ExceptionHandlingMiddleware
    BaseHTTPMiddleware <|-- LogOriginMiddleware

    Logger <.. ExceptionHandlingMiddleware : uses logger.error
    Logger <.. LogOriginMiddleware : uses logger.info

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File-Level Changes

Change	Details	Files
Centralize and adjust Cloud Run CORS origin configuration and usage.	Move cloud_origins and cloud_origin_regex definitions to the top-level of backend/main.py so they can be reused across environments. Keep and slightly cleanup the explicit list of allowed Cloud Run origins and the flexible regex r"https://query-craft-frontend.*\.run.app" to cover multiple regional/subdomain variants. Use the shared cloud_origins and cloud_origin_regex consistently in both production and non-production CORS middleware configuration blocks.	backend/main.py
Reorder middleware registration to make request processing and CORS debugging behavior explicit.	Document the intended middleware execution order (LogOrigin -> CORS -> Exception -> PathRewrite) in comments. Register PathRewriteMiddleware first, then ExceptionHandlingMiddleware, then CORS middleware (production vs non-production branches), and finally LogOriginMiddleware so that it runs outer-most before CORS. Clarify in comments how this order affects CORS handling, exception handling, and logging, including the interaction with the @app.middleware("http") error logging middleware.	backend/main.py
Add origin logging middleware for CORS debugging and standardize middleware logging usage.	Create a module-level logger via get_logger("backend.middleware") for reuse across middleware classes. Update ExceptionHandlingMiddleware to use the shared logger instead of instantiating a logger on each exception. Introduce LogOriginMiddleware that logs the Origin header, request path, and HTTP method for incoming requests before delegating to downstream middleware.	backend/common/middleware.py backend/main.py

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[sourcery-ai]

Hey - I've left some high level feedback:

• In production CORS config you only use allow_origins=cloud_origins and never apply cloud_origin_regex, which seems to contradict the intent in the description; consider adding allow_origin_regex=cloud_origin_regex there as well if you want new Cloud Run regional domains to be automatically accepted.
• The new LogOriginMiddleware will log every request’s origin, path, and method in all environments; you may want to gate this behind an environment flag or lower log level to avoid excessive log volume or unintentionally persisting sensitive request patterns in production.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In production CORS config you only use `allow_origins=cloud_origins` and never apply `cloud_origin_regex`, which seems to contradict the intent in the description; consider adding `allow_origin_regex=cloud_origin_regex` there as well if you want new Cloud Run regional domains to be automatically accepted.
- The new `LogOriginMiddleware` will log every request’s origin, path, and method in all environments; you may want to gate this behind an environment flag or lower log level to avoid excessive log volume or unintentionally persisting sensitive request patterns in production.

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