GitHub announced in November 2019 the deprecation of several authentication methods.

This impacts the SourceGitHub plugin, which currently uses an access_token query parameter to authenticate.

Authenticating using query parameters

GitHub is deprecating authentication to the GitHub API using query parameters, such as using a access_token query parameter for OAuth user authentication or a client_id/client_secret query parameter for OAuth application authentication. All authentication to the GitHub API should be done using HTTP basic authentication.