(C) 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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#include <C_CkFileAccess.h>
#include <C_CkAuthGoogle.h>
#include <C_CkSocket.h>
#include <C_CkStringBuilder.h>

void ChilkatSample(void)
    {
    HCkFileAccess fac;
    const char *jsonKey;
    HCkAuthGoogle gAuth;
    HCkSocket tlsSock;
    BOOL success;
    HCkStringBuilder sbToken;

    // 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.
    fac = CkFileAccess_Create();
    jsonKey = CkFileAccess_readEntireTextFile(fac,"qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8");
    if (CkFileAccess_getLastMethodSuccess(fac) != TRUE) {
        printf("%s\n",CkFileAccess_lastErrorText(fac));
        CkFileAccess_Dispose(fac);
        return;
    }

    // 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"
    // 	}

    gAuth = CkAuthGoogle_Create();
    CkAuthGoogle_putJsonKey(gAuth,jsonKey);

    // Choose a scope.
    CkAuthGoogle_putScope(gAuth,"https://www.googleapis.com/auth/cloud-platform");

    // Request an access token that is valid for this many seconds.
    CkAuthGoogle_putExpireNumSeconds(gAuth,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.)
    CkAuthGoogle_putSubEmailAddress(gAuth,"");

    // 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.
    tlsSock = CkSocket_Create();
    success = CkSocket_Connect(tlsSock,"www.googleapis.com",443,TRUE,5000);
    if (success != TRUE) {
        printf("%s\n",CkSocket_lastErrorText(tlsSock));
        CkFileAccess_Dispose(fac);
        CkAuthGoogle_Dispose(gAuth);
        CkSocket_Dispose(tlsSock);
        return;
    }

    // Send the request to obtain the access token.
    success = CkAuthGoogle_ObtainAccessToken(gAuth,tlsSock);
    if (success != TRUE) {
        printf("%s\n",CkAuthGoogle_lastErrorText(gAuth));
        CkFileAccess_Dispose(fac);
        CkAuthGoogle_Dispose(gAuth);
        CkSocket_Dispose(tlsSock);
        return;
    }

    // Examine the access token:
    printf("Access Token: %s\n",CkAuthGoogle_accessToken(gAuth));

    // We're going to save this access token to a file to be used
    // by other examples.
    sbToken = CkStringBuilder_Create();
    CkStringBuilder_Append(sbToken,CkAuthGoogle_accessToken(gAuth));
    CkStringBuilder_WriteFile(sbToken,"qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8",FALSE);


    CkFileAccess_Dispose(fac);
    CkAuthGoogle_Dispose(gAuth);
    CkSocket_Dispose(tlsSock);
    CkStringBuilder_Dispose(sbToken);

    }