(Swift 3,4,5...) 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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func chilkatTest() {
    // 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.
    let fac = CkoFileAccess()!
    var jsonKey: String? = fac.readEntireTextFile("qa_data/firebase/firebase-chilkat-firebase-adminsdk-n28n4-1b664ee163.json", charset: "utf-8")
    if fac.lastMethodSuccess != true {
        print("\(fac.lastErrorText!)")
        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"
    // } 
    // 

    let gAuth = CkoAuthGoogle()!
    gAuth.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.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.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.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.
    let tlsSock = CkoSocket()!
    var success: Bool = tlsSock.connect("www.googleapis.com", port: 443, ssl: true, maxWaitMs: 5000)
    if success != true {
        print("\(tlsSock.lastErrorText!)")
        return
    }

    // Send the request to obtain the access token.
    success = gAuth.obtainAccessToken(tlsSock)
    if success != true {
        print("\(gAuth.lastErrorText!)")
        return
    }

    // Examine the access token:
    print("Firebase Access Token: \(gAuth.accessToken!)")

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

}