oauth: Allow auth_url and token_url to be set in the config file

If set in the config file, these override the ones configured into the
remote.  This enables alternative oauth servers to be used for all
oauth remotes.  This can only be altered by editing the config file
for the moment.

fs/config.go

@@ -44,6 +44,12 @@ const (
 	// ConfigClientSecret is the config key used to store the client secret
 	ConfigClientSecret = "client_secret"
 
+	// ConfigAuthURL is the config key used to store the auth server endpoint
+	ConfigAuthURL = "auth_url"
+
+	// ConfigTokenURL is the config key used to store the token server endpoint
+	ConfigTokenURL = "token_url"
+
 	// ConfigAutomatic indicates that we want non-interactive configuration
 	ConfigAutomatic = "config_automatic"
 )

oauthutil/oauthutil.go

@@ -209,6 +209,16 @@ func overrideCredentials(name string, origConfig *oauth2.Config) (config *oauth2
 		config.ClientSecret = ClientSecret
 		changed = true
 	}
+	AuthURL := fs.ConfigFileGet(name, fs.ConfigAuthURL)
+	if AuthURL != "" {
+		config.Endpoint.AuthURL = AuthURL
+		changed = true
+	}
+	TokenURL := fs.ConfigFileGet(name, fs.ConfigTokenURL)
+	if TokenURL != "" {
+		config.Endpoint.TokenURL = TokenURL
+		changed = true
+	}
 	return config, changed
 }