https://codeberg.org/cuchazinteractive/burgerid
This doc is waaaay out of date though. I've done a lot of work since it was written and I really should update it.
For instance, the identity public and private parts have separate files now. version 1 of the identities is based on ECC now, not RSA. And the (server-side) library does now provide authentication functions, since that's tricky to get right when you have key rotations and revocations in the mix. And the examples are all completely wrong now. =P
But, the doc should still give you the big-picture goals of the project at least, even if a lot of the details are wrong.
Let me know if you have any questions.