I'm using this openid client for implementing an SSO flow.

The error that I'm getting is that at_hash values do not match. Example:

what the client is expecing: AIRY7ahdicSipVPIZtciog

what the client is getting from the JWT in the SSO flow: AIRY7ahdicSipVPIZtciog==

I know the problem is in the base64 encoding. I know that what I'm using is compliant with the standard.

What should I do? I was digging around the client code and I know what I have to change in order to "make it work". It's the first few lines in this file, but I'm not doing that. I think the problem is in the way the third party has their SSO flow configured and I don't think I can convince them to change that.