This is a working RelMeAuth prototype that uses Web sign-in for logging-in.
Enter your personal web address, click Sign-in, and see what happens.
This checkbox is a metaphorical big red button you're supposed to try ignoring, or dare to click. It's only here because the OAuth allow permission page of the presumed destination doesn't have it, which is really where it should be (so we don't have to presume the destination).
It is likely there are still errors and any issues should be reported on the GitHub Project Page. This code is written by @themattharris and @t. It uses a modified OAuth PHP library.