Google Cloud FCM

Firebase Cloud Messaging (FCM) is a cross-platform messaging solution that lets you reliably send messages at no cost.

 

Using FCM, you can notify a client app that new email or other data is available to sync. You can send notification messages to drive user re-engagement and retention. For use cases such as instant messaging, a message can transfer a payload of up to 4096 bytes to a client app.

 

The component supports the HTTP v1 API.

Authorization

Google FCM component client can login to Google Servers using the following methods:

 

• gcaOAuth2: OAuth2 protocol
• gcaJWT: JWT tokens.

 

OAuth2

 

The login is done using a web browser where the user logs in with their own account and authorizes the FCM requests.

 

• GoogleCloudOptions.OAuth2.ClientId: is the ClientID provided by Google to Authenticate through OAuth2 protocol.
• GoogleCloudOptions.OAuth2.ClientSecret: is the Client Secret string provided by Google to Authenticate through OAuth2 protocol.
• GoogleCloudOptions.OAuth2.Scope: is the scope of OAuth2, usually there is no need to modify the default value unless you need to get more access than default.
• GoogleCloudOptions.OAuth2.LocalIP: the OAuth2 protocol requires a local server listening for the response from the authentication server. This is the IP or DNS name. By default, it is 127.0.0.1.
• GoogleCloudOptions.OAuth2.LocalPort: Local server listening port.
• GoogleCloudOptions.OAuth2.RedirectURL: if you need to set a redirect URL different from LocalPort + LocalIP, you can set it in this property (example: http://127.0.0.1:8080/oauth2).

 

Service Accounts

 

The login is done by signing the requests using a private key provided by Google. This method is recommended for automated services or applications without user interaction.

 

• GoogleCloudOptions.JWT.ClientEmail: the client email name provided when creating the new service account. "client_email" node in the JSON configuration file.
• GoogleCloudOptions.JWT.Subject: the client email name provided when creating the new service account. "client_email" node in the JSON configuration file.
• GoogleCloudOptions.JWT.PrivateKeyId: the Private Key ID provided by Google. "private_key_id" node in the JSON configuration file.
• GoogleCloudOptions.JWT.PrivateKey: the Private Key certificate provided by Google. "private_key" node in the JSON configuration file.

 

TLS Options

 

Firebase Cloud Messaging connections can be tuned through the TLSOptions property.

• TLSOptions.IOHandler: choose the TLS stack that will be used (OpenSSL, SChannel...).
• TLSOptions.Version: request a specific TLS protocol version required by your project.
• TLSOptions.VerifyCertificate: enforce server certificate validation when connecting to Google.
• TLSOptions.OpenSSL_Options.LibPath: define where the OpenSSL runtime libraries are deployed.
• TLSOptions.SChannel_Options.UseLegacyCredentials: enable it when Windows SChannel requires legacy credential negotiation.

 

Example configuration:

oFCM := TsgcHTTPGoogleCloud_FCM_Client.Create(nil);
oFCM.TLSOptions.IOHandler := iohOpenSSL;
oFCM.TLSOptions.Version := tls1_3;
oFCM.TLSOptions.VerifyCertificate := True;
oFCM.TLSOptions.OpenSSL_Options.LibPath := oslpDefaultFolder;

 

When a new service account is created, you can download a JSON file with all configurations. This file can be processed by the FCM component, just call the method LoadSettingsFromFile and pass the JSON filename as argument.

 

 

Most common uses

• Configuration
  • Google OAuth2 Keys
  • Service Accounts

 

Google FCM Client

 

OAuth2

 

In order to work with the Google FCM API, the sgcWebSockets FCM component uses OAuth2 as the default authentication method, so first you must set your ClientId and ClientSecret from your Google account.

 

oFCM:= TsgcHTTPGoogleCloud_FCM_Client.Create(nil);
oFCM.GoogleCloudOptions.Authorization := gcaOAuth2;
oFCM.GoogleCloudOptions.OAuth2.ClientId := '... your google client id...';
oFCM.GoogleCloudOptions.OAuth2.ClientSecret := '... your google client secret...';

 

Service Accounts

 

Service Accounts require building a JWT and passing it as an authorization token.

 

oFCM := TsgcHTTPGoogleCloud_FCM_Client.Create(nil);
oFCM.GoogleCloudOptions.Authorization := gcaJWT;
oFCM.GoogleCloudOptions.JWT.ClientEmail := '...google email...';
oFCM.GoogleCloudOptions.JWT.Subject := '...google email...';
oFCM.GoogleCloudOptions.JWT.PrivateKeyId := '...private key id...';
oFCM.GoogleCloudOptions.JWT.PrivateKey.Lines.Text := '...private key certificate...';

This is required in order to get an Authorization Token Key from Google which will be used for all Rest API calls.

 

All methods return a response, which may be successful or return an error.

 

Send Message

Use the method SendMessage to send a notification message. The function has 2 arguments:

 

1. Project: is the project id of your google cloud account.
2. Payload: is the json text message. Example:

 

{
  "message": {
    "topic": "news",
    "notification": {
      "title": "Breaking News",
      "body": "New news story available."
    },
    "data": {
      "story_id": "story_12345"
    }
  }
}