It looks like you need to avoid creating & using iphone shortcut icon (on your iphone desktop) for tagbirds website will block social auth.
Maybe any desktop “shortcut” icon is sandboxed from any other process on your iphone such that the shortcut icon has no access to the secret token / key for oauth stored with your browser?
How iPhone “bookmarks” work: I think you must use Safari (native browser for iPhone and Apple products), via the “Safari app” on your iPhone; select bookmark e.g. “tagbirds.com”, go to site, just select “GitHub” to use GitHub social auth for tagbirds.com; you should only have to enter your GitHub creds one time only; in future, when using the same physical iPhone you, just select “GitHub” again and you should be automatically logged in / authenticated (no entering of GitHub creds again.
But not sure it django-allauth “auto-logs” correctly like this for Safari bookmark. Works that way for Chome/google app, but chime/google app bookmarks are very hard for me to use and/or understand?