Add refreshTokenUrl to enable automatic OAuth token refresh

[jacobhaug]

Problem

Users are experiencing OAuth token expiration errors every 1-2 weeks, requiring manual reconnection of their Basecamp OAuth credentials. The error message "Missing code query parameter" appears when access tokens expire, forcing users to manually reconnect through the n8n UI.

Solution

Added the refreshTokenUrl property to the OAuth2 credentials configuration. This enables n8n's built-in OAuth2Api base class to automatically refresh expired access tokens using the stored refresh token, eliminating the need for manual reconnection.

Changes

• Added refreshTokenUrl property to Basecamp4OAuth2Api.credentials.ts
• Set to the same endpoint as accessTokenUrl: https://launchpad.37signals.com/authorization/token?type=web_server

How It Works

When n8n detects an expired access token, it will:

1. Automatically use the stored refresh token
2. Make a request to the refreshTokenUrl endpoint
3. Obtain a new access token (and potentially a new refresh token)
4. Update the stored credentials automatically
5. Retry the original API request

This all happens transparently in the background without user intervention.

Testing

• Verified the refresh token URL matches Basecamp's token endpoint
• Confirmed compatibility with n8n's OAuth2Api base class

User Impact

After this change is merged and users update to the new version:

• Users will need to reconnect their OAuth connection once to ensure a refresh token is properly stored
• After that initial reconnection, tokens will refresh automatically
• No more manual reconnection required every 1-2 weeks

References

• Basecamp API Authentication Documentation
• OAuth 2.0 Refresh Token Flow: https://oauth.net/2/refresh-tokens/

Ticket: #2

[afroximity]

Nice! I confirm that this is working.

[jacobhaug]

@ryanrhughes can you review and merge please?