Troubleshooting OAuth Redirects to Unexpected Applications in Flask and Strava API Integrations

Implementing third-party authentication can significantly enhance your application’s user experience, but it sometimes introduces perplexing issues. One such problem occurs when a Flask-based web application utilizing the Strava API encounters unexpected OAuth redirect behaviors—specifically, the authorization process pointing to a different application altogether.

In this article, we’ll explore a common scenario where a Flask backend, designed for secure user authentication via Strava, unexpectedly redirects users to an unrelated application’s authorization page. We’ll also discuss potential causes and best practices to resolve such issues.

Understanding the Issue

Imagine developing a web app with a Flask backend and a Vue.js frontend that leverages the Strava API for user authentication. The process involves constructing an authorization URL using your application’s Client ID, prompting users to grant access to their Strava data.

However, instead of directing users to your app’s authorization page, the redirect unexpectedly points to a different application’s page—say, “Simon’s Journey Viz”—which has its own client credentials and permissions. This mismatch causes confusion and hampers user authentication.

Common Causes and Diagnostic Steps

1. Incorrect or Cached OAuth URLs

2. Issue: Browsers or servers caching old authorization URLs can lead to redirects pointing to outdated or incorrect apps.

3. Solution: Clear your browser cache and ensure your app generates fresh authorization URLs each time. Verify that your backend constructs the URL with your current Client ID.

4. Misconfigured Client Credentials

5. Issue: Using wrong or outdated Client IDs and Secrets within the Flask application can cause the authorization flow to reference different applications.

6. Solution: Double-check your environment variables and configuration files to ensure the credentials correspond to your intended application. Remember, these are sensitive and should be kept secure.

7. Strava API Application Management

8. Issue: Sometimes, Strava’s developer portal or API management interface might show unexpected behaviors, or you may lack access to delete or modify existing apps.

9. Solution: Verify your app settings directly on Strava’s developer dashboard. If you cannot manage your app, ensure you’re logged into the correct account and confirm the app’s configuration matches your expectations.

10. Incorrect OAuth URL Generation

11. Issue: The backend code responsible for creating the authorization URL might inadvertently reference the wrong client credentials or parameters.

12. Solution: Review your app.py or