Problem authenticating on mastodon.social

When I use the Keybase client to authenticate on mastodon.social I get the following error.

Start by reviewing the Keybase client authentication flow and reproducing the reported failure against mastodon.social using the attached screenshot as the observed result. Determine which authentication step produces the error, then verify that the flow completes successfully and add or update coverage if an existing authentication test entry point is found.

Written by the indexing model from the issue text.