Improvement: Provide Immediate Feedback When SSO Authentication Fails in Browser

Description
When a user attempts to sign in with SSO in the Mergin Maps plugin and the authentication in the browser fails, no information is sent back to the QGIS plugin about this unsuccessful authorization. Currently, the plugin waits for 2 minutes for a response and then the login fails without a specific error message about what went wrong in the browser. This creates a poor user experience as the user has to wait unnecessarily without knowing what's happening.

Environment
Staging

Application (+ app version, build, operating system)

• QGIS version: 3.40.5-Bratislava
• Plugin version: 2025.1.1
• OS: macOS, Sequoia 15.5

Steps to reproduce

1. Open QGIS and the Mergin Maps plugin
2. Attempt to sign in using the SSO option
3. In the opened browser window, fail to authenticate (wrong credentials, cancel the process, etc.)
4. Observe that the plugin continues to wait for authentication with no feedback
5. After approximately 2 minutes, the login finally fails in the plugin

Actual results

• When SSO authentication fails in the browser, the plugin does not receive immediate notification
• The plugin waits for the full timeout period (2 minutes) before showing a login failure
• No specific error message indicating what went wrong during the browser authentication

Expected results

• The plugin should receive immediate notification when SSO authentication fails in the browser
• A clear error message should be displayed to the user explaining what went wrong
• The plugin should not wait for the full timeout period if authentication has already failed

Screenshots or logs

https://github.com/user-attachments/assets/7a36ae64-6774-403c-9ad6-e3db68082ea2

Conclusion
Created by GitHub Copilot and supervised by a human test analyst.

Start at the Mergin Maps QGIS plugin's SSO sign-in flow and trace how browser authentication results and the two-minute timeout are handled. Reproduce a failed or cancelled browser login, then verify that the plugin receives the failure immediately and displays a clear error instead of waiting for the timeout.