(Lianja) Get Google Cloud Storage Access Token using Service Account JSON Private Key

Demonstrates how to get a Google Cloud Storage access token using a JSON service account private key. Obtaining an access token for a service account requires no user interaction (it does not require a browser, nor callback URI's, etc.).

When an access token expires, an application can be (and should be) designed to automatically fetch a new access token.

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

// First load the JSON key into a string.
loFac = createobject("CkFileAccess")
lcJsonKey = loFac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
if (loFac.LastMethodSuccess <> .T.) then
    ? loFac.LastErrorText
    release loFac
    return
endif

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

// 	{
// 	  "type": "service_account",
// 	  "project_id": "chilkattest-1350",
// 	  "private_key_id": "fa2e36ee26986eab628b59868af8bec1d1c64c38",
// 	  "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvgIjFa...28N64N2n1E4FYzBZjSdy\n-----END PRIVATE KEY-----\n",
// 	  "client_email": "598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a@developer.gserviceaccount.com",
// 	  "client_id": "598922945226-00rb0ppfg0snd9jo7bhvd4v17jtj2d3a.apps.googleusercontent.com",
// 	  "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/x509/598922945226-00rb0ppfg0sndajo6bhvd4v17jtj2d3a%40developer.gserviceaccount.com"
// 	}

loGAuth = createobject("CkAuthGoogle")
loGAuth.JsonKey = lcJsonKey

// Choose a scope.
loGAuth.Scope = "https://www.googleapis.com/auth/cloud-platform"

// Request an access token that is valid for this many seconds.
loGAuth.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.)
loGAuth.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.
loTlsSock = createobject("CkSocket")
llSuccess = loTlsSock.Connect("www.googleapis.com",443,.T.,5000)
if (llSuccess <> .T.) then
    ? loTlsSock.LastErrorText
    release loFac
    release loGAuth
    release loTlsSock
    return
endif

// Send the request to obtain the access token.
llSuccess = loGAuth.ObtainAccessToken(loTlsSock)
if (llSuccess <> .T.) then
    ? loGAuth.LastErrorText
    release loFac
    release loGAuth
    release loTlsSock
    return
endif

// Examine the access token:
? "Access Token: " + loGAuth.AccessToken

// We're going to save this access token to a file to be used
// by other examples.
loSbToken = createobject("CkStringBuilder")
loSbToken.Append(loGAuth.AccessToken)
loSbToken.WriteFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8",.F.)


release loFac
release loGAuth
release loTlsSock
release loSbToken