Firebase Cloud Messaging API (#81)

* Adding Firebase Cloud Messaging (#62)

* initial commit for adding Firebase Cloud Messaging

* add validator

* use http const in messaging test

* add client version header for stats

* init integration test

* add integration test (validated on IOS today)

* add comment with URL to enable Firebase Cloud Messaging API

* fix broken test

* add integration tests

* accept a Message instead of RequestMessage + and rename method + send  / sendDryRun

* update fcm url

* rollback url endpoint

* fix http constants, change responseMessage visibility, change map[string]interface{} as map[string]string

* fix http constants

* fix integration tests

* fix APNS naming

* add validators

* Added APNS types; Updated tests

* Added more tests; Fixed APNS serialization

* Updated documentation

* Improved error handling inFCM

* Added utils file

* Updated integration tests

* Implemented topic management operations

* Added integration tests

* Updated CHANGELOG

* Addressing code review comments

* Supporting 0 valued Aps.Badge

* Addressing some review comments

* Removed some unused vars

* Accepting prefixed topic names (#84)

* Accepting prefixed topic named

* Added a comment

* Using new FCM error codes (#89)

Author: hiranya911

CHANGELOG.md

@@ -41,6 +41,21 @@
 
 ### Authentication
 
+- [added] A new [`VerifyIDTokenAndCheckRevoked()`](https://godoc.org/firebase.google.com/go/auth#Client.VerifyIDToken)
+  function has been added to check for revoked ID tokens.
+- [added] A new [`RevokeRefreshTokens()`](https://godoc.org/firebase.google.com/go/auth#Client.RevokeRefreshTokens)
+  function has been added to invalidate all refresh tokens issued to a user.
+- [added] A new property `TokensValidAfterMillis` has been added to the
+  ['UserRecord'](https://godoc.org/firebase.google.com/go/auth#UserRecord)
+  type, which stores the time of the revocation truncated to 1 second accuracy.
+
+### Cloud Messaging
+
+- [feature] Added the `messaging` package for sending Firebase notifications
+  and managing topic subscriptions.
+
+### Authentication
+
 - [added] A new [`VerifyIDTokenAndCheckRevoked()`](https://godoc.org/firebase.google.com/go/auth#Client.VerifyIDToken)
   function has been added to check for revoked ID tokens.
 - [added] A new [`RevokeRefreshTokens()`](https://godoc.org/firebase.google.com/go/auth#Client.RevokeRefreshTokens)

internal/internal.go

@@ -102,6 +102,13 @@ type MockTokenSource struct {
 	AccessToken string
 }
 
+// MessagingConfig represents the configuration of Firebase Cloud Messaging service.
+type MessagingConfig struct {
+	Opts      []option.ClientOption
+	ProjectID string
+	Version   string
+}
+
 // Token returns the test token associated with the TokenSource.
 func (ts *MockTokenSource) Token() (*oauth2.Token, error) {
 	return &oauth2.Token{AccessToken: ts.AccessToken}, nil