Add monkey patch for OIDC conformance tests

[kwajiehao]

To ensure that our SDKs are conformant with the OIDC spec, we should run conformance tests against the OIDC conformance test server. To do that, we need to modify our SDK to point to the OIDC test server. We have already done this for the nodejs SDK (see here), but we will need to do it for the Python SDK as well