OIDC Regression

[russjones]

Problem

In #882, we patched go-oidc to fallback to standard encoding if we failed to decode with URL encoding. When we moved to the new dependency management tool in #1218 it looks like we lost this patch.

Proposed Solution

It looks like we have a fork with this patch, we just have to update dep to point to our fork: https://github.com/gravitational/go-oidc