Just in case you are using GitHub for login here you may have received an email with the subject like “[GitHub API] Deprecation notice”
We are on it and an update with a fix should be applied soon. Plus, the deprecation is not until July so there is plenty of time.
In case you are curious, you can track it on meta.discourse via this topic:
This should be sorted now. Let me know if you still get any issues with github logins!