ParseKey converts the binary contents of a private key file to an *rsa.PrivateKey.

HTTPClient is the context key to use with golang.org/x/net/context's WithValue function to associate an *http.Client value with a context.

ContextKey is just an empty struct.

ErrorTransport returns the specified error on RoundTrip.

Token represents the crendentials used to authorize the requests to access protected resources on the OAuth 2.0 provider's backend.

ContextClientFunc is a func which tries to return an *http.Client given a Context value.