Set userid prefix and header for IAP. (#3996)
Set userid prefix and header for IAP. (#3996)

* When using IAP, we need to configure various applications to look at
the correct header and prefix so that they get the identity correctly.

Related to #3986
kubeflow/kubeflow,kubeflow/kubeflow,kubeflow/kubeflow,kubeflow/kubeflow,kubeflow/kubeflow,kubeflow/kubeflow