URL parse auth endpoints to normalize hostname to lowercase.

It is possible for a middlebox to lowercase the URL at somepoint causing a
lookup in the auth challenges table to fail.  Lowercase hostname before
using as keys to challenge map.

Signed-off-by: Richard Scothern <richard.scothern@gmail.com>

docs/client/auth/session.go

@@ -67,9 +67,7 @@ func (ea *endpointAuthorizer) ModifyRequest(req *http.Request) error {
 		Path:   req.URL.Path[:v2Root+4],
 	}
 
-	pingEndpoint := ping.String()
-
-	challenges, err := ea.challenges.GetChallenges(pingEndpoint)
+	challenges, err := ea.challenges.GetChallenges(ping)
 	if err != nil {
 		return err
 	}