Implement OAuth in middleware for authentication

Currently, header-based authentication is outdated and poses a security risk. Adding OAuth support to the middleware will improve security with modern, token-based authentication.

The issue mentions middleware and replacing header-based auth with OAuth. Look for authentication middleware in the codebase, likely in a middleware or auth module. Research FastAPI OAuth integrations (like OAuth2PasswordBearer) to understand the pattern. The goal is to implement OAuth flow in the existing middleware structure, ensuring tokens are validated.

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