auth: Refactor how authentication methods are passed to server/auth library.

server/auth/authtest/state.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package authtest
 
 import (
         "net"
 
         "github.com/luci/luci-go/server/auth"
@@ skipping 34 matching lines @@
         PeerIdentityOverride identity.Identity
 
         // PeerIPOverride may be set for PeerIP() to return custom value.
         //
         // By default PeerIP() returns "127.0.0.1".
         PeerIPOverride net.IP
 }
 
 var _ auth.State = (*FakeState)(nil)
 
+// Authenticator is part of State interface.
+func (s *FakeState) Authenticator() *auth.Authenticator {
+        return &auth.Authenticator{
+                Methods: []auth.Method{
+                        &FakeAuth{User: s.User()},
+                },
+        }
+}
+
 // DB is part of State interface.
 func (s *FakeState) DB() authdb.DB {
         if s.FakeDB != nil {
                 return s.FakeDB
         }
         return &FakeErroringDB{
                 FakeDB: FakeDB{s.User().Identity: s.IdentityGroups},
                 Error:  s.Error,
         }
 }
 
 // Method is part of State interface.
 func (s *FakeState) Method() auth.Method {
-        return &FakeAuth{
-                User: s.User(),
-        }
+        return s.Authenticator().Methods[0]
 }
 
 // User is part of State interface.
 func (s *FakeState) User() *auth.User {
         ident := identity.AnonymousIdentity
         if s.Identity != "" {
                 ident = s.Identity
         }
         return &auth.User{
                 Identity: ident,
                 Email:    ident.Email(),
         }
 }
 
 // PeerIdentity is part of State interface.
 func (s *FakeState) PeerIdentity() identity.Identity {
         if s.PeerIdentityOverride == "" {
                 return s.User().Identity
         }
         return s.PeerIdentityOverride
 }
 
 // PeerIP is part of State interface.
 func (s *FakeState) PeerIP() net.IP {
         if s.PeerIPOverride == nil {
                 return net.ParseIP("127.0.0.1")
         }
         return s.PeerIPOverride
 }