(C++) Get Firebase Access Token from JSON Service Account Private Key

Demonstrates how to get a Firebase access token using a JSON service account private key. Your Firebase service account can be used to authenticate multiple Firebase features, such as Database, Storage and Auth, programmatically.

A Firebase JSON service account private key can be created in the Firebase settings/admin portion of the console.firebase.google.com site as shown here:

Scroll down to see the example code...

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#include <CkFileAccess.h>
#include <CkAuthGoogle.h>
#include <CkSocket.h>

void ChilkatSample(void)
    {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // First load the Firebase JSON private key into a string.
    CkFileAccess fac;
    const char *jsonKey = fac.readEntireTextFile("qa_data/firebase/firebase-chilkat-firebase-adminsdk-n28n4-1b664ee163.json","utf-8");
    if (fac.get_LastMethodSuccess() != true) {
        std::cout << fac.lastErrorText() << "\r\n";
        return;
    }

    // A Firebase JSON private key should look something like this:

    // { 
    //   "type": "service_account",
    //   "project_id": "firebase-chilkat",
    //   "private_key_id": "1c664ee164907413c91ddefcf5b765ecba8779e2",
    //   "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvQIBA ... Ya2UZii/lXn73/ZOK8=\n-----END PRIVATE KEY-----\n",
    //   "client_email": "firebase-adminsdk-n28n4@firebase-chilkat.iam.gserviceaccount.com",
    //   "client_id": "134846322329335418431",
    //   "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    //   "token_uri": "https://accounts.google.com/o/oauth2/token",
    //   "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    //   "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/firebase-adminsdk-n28n4%40firebase-chilkat.iam.gserviceaccount.com"
    // } 
    // 

    CkAuthGoogle gAuth;
    gAuth.put_JsonKey(jsonKey);

    // Choose a scope.
    // The scope could be "https://www.googleapis.com/auth/firebase.database"
    // or a space-delimited list of scopes:
    // "https://www.googleapis.com/auth/firebase.database https://www.googleapis.com/auth/userinfo.email"

    gAuth.put_Scope("https://www.googleapis.com/auth/firebase.database https://www.googleapis.com/auth/userinfo.email");

    // Request an access token that is valid for this many seconds.
    gAuth.put_ExpireNumSeconds(3600);

    // If the application is requesting delegated access:
    // The email address of the user for which the application is requesting delegated access,
    // then set the email address here. (Otherwise leave it empty.)
    gAuth.put_SubEmailAddress("");

    // Connect to www.googleapis.com using TLS (TLS 1.2 is the default.)
    // The Chilkat socket object is used so that the connection can be established
    // through proxies or an SSH tunnel if desired.
    CkSocket tlsSock;
    bool success = tlsSock.Connect("www.googleapis.com",443,true,5000);
    if (success != true) {
        std::cout << tlsSock.lastErrorText() << "\r\n";
        return;
    }

    // Send the request to obtain the access token.
    success = gAuth.ObtainAccessToken(tlsSock);
    if (success != true) {
        std::cout << gAuth.lastErrorText() << "\r\n";
        return;
    }

    // Examine the access token:
    std::cout << "Firebase Access Token: " << gAuth.accessToken() << "\r\n";

    // Save the token to a file (or wherever desired).  This token is valid for 1 hour.
    fac.WriteEntireTextFile("qa_data/tokens/firebaseToken.txt",gAuth.accessToken(),"utf-8",false);
    }