[v1] identity: use AuthOptionsBuilder for v2 auth

Rather than creating a tokens2.AuthOptions inside the authentication
flow for identity v2, allow any structure that implements the
tokens2.AuthBuilderOptions interface to be used. The
gophercloud.AuthOptions already implements this interface so there
is no change to the API. To avoid any API change, add
AuthenticateV2Ext() as a version of AuthenticateV2() accepting the
interface. This will allow an out of tree identity v2 auth mechanism
to be implemented, just like the v3. fixes gophercloud#2651. ref gophercloud#1330.

openstack/client.go

@@ -116,7 +116,11 @@ func AuthenticateV2(client *gophercloud.ProviderClient, options gophercloud.Auth
 	return v2auth(client, "", options, eo)
 }
 
-func v2auth(client *gophercloud.ProviderClient, endpoint string, options gophercloud.AuthOptions, eo gophercloud.EndpointOpts) error {
+func AuthenticateV2Ext(client *gophercloud.ProviderClient, options tokens2.AuthOptionsBuilder, eo gophercloud.EndpointOpts) error {
+	return v2auth(client, "", options, eo)
+}
+
+func v2auth(client *gophercloud.ProviderClient, endpoint string, options tokens2.AuthOptionsBuilder, eo gophercloud.EndpointOpts) error {
 	v2Client, err := NewIdentityV2(client, eo)
 	if err != nil {
 		return err
@@ -126,17 +130,7 @@ func v2auth(client *gophercloud.ProviderClient, endpoint string, options gopherc
 		v2Client.Endpoint = endpoint
 	}
 
-	v2Opts := tokens2.AuthOptions{
-		IdentityEndpoint: options.IdentityEndpoint,
-		Username:         options.Username,
-		Password:         options.Password,
-		TenantID:         options.TenantID,
-		TenantName:       options.TenantName,
-		AllowReauth:      options.AllowReauth,
-		TokenID:          options.TokenID,
-	}
-
-	result := tokens2.Create(v2Client, v2Opts)
+	result := tokens2.Create(v2Client, options)
 
 	err = client.SetTokenAndAuthResult(result)
 	if err != nil {
@@ -148,16 +142,30 @@ func v2auth(client *gophercloud.ProviderClient, endpoint string, options gopherc
 		return err
 	}
 
-	if options.AllowReauth {
+	// use if the client's ReauthFunc is set to avoid needing to copy the AuthOptions and mutating the AllowReauth value
+	// when creating the reauthentication function below. this allows breaking of the loop without v2auth having to have
+	// knowledge of the supplied struct, allowing for out of tree extensions
+	if client.ReauthFunc != nil {
 		// here we're creating a throw-away client (tac). it's a copy of the user's provider client, but
 		// with the token and reauth func zeroed out. combined with setting `AllowReauth` to `false`,
 		// this should retry authentication only once
 		tac := *client
 		tac.SetThrowaway(true)
 		tac.ReauthFunc = nil
 		tac.SetTokenAndAuthResult(nil)
-		tao := options
-		tao.AllowReauth = false
+		var tao tokens2.AuthOptionsBuilder
+		switch ot := options.(type) {
+		case *gophercloud.AuthOptions:
+			o := *ot
+			o.AllowReauth = false
+			tao = &o
+		case *tokens2.AuthOptions:
+			o := *ot
+			o.AllowReauth = false
+			tao = &o
+		default:
+			tao = options
+		}
 		client.ReauthFunc = func() error {
 			err := v2auth(&tac, endpoint, tao, eo)
 			if err != nil {