(MFC) Refresh Access Token on 401 Unauthorized and Retry

Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.)

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkStringBuilder.h>
#include <CkHttp.h>
#include <CkBinData.h>
#include <CkFileAccess.h>
#include <CkAuthGoogle.h>
#include <CkSocket.h>

void ChilkatSample(void)
    {
    CkString strOut;

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

    // This example uses a previously obtained access token having permission for the 
    // scope "https://www.googleapis.com/auth/cloud-platform"

    // In this example, Get Google Cloud Storage OAuth2 Access Token, 
    // the service account access token was saved to a text file.  This example fetches the access token from the file..
    CkStringBuilder sbToken;
    bool success = sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8");
    if (success == false) {
        strOut.append("Failed to load access token.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    CkHttp http;

    http.put_AuthToken(sbToken.getAsString());

    // Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
    http.SetUrlVar("bucket_name","chilkat-ocean");
    http.SetUrlVar("object_name","starfish.jpg");
    const char *url = "https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media";

    // If there is an error response, then we didn't actually download the file data,
    // but instead we downloaded an error response..
    CkBinData fileData;
    success = http.DownloadBd(url,fileData);
    int responseCode = http.get_LastStatus();
    if ((success == false) && (responseCode != 401)) {
        strOut.append(http.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    if (responseCode == 401) {
        strOut.append("Received 401 Unauthorized response. Attempting to refresh the access token...");
        strOut.append("\r\n");

        // May be that the access token expired.
        // Load our JSON key and request a new access token, then retry the original request.
        CkFileAccess fac;
        const char *jsonKey = fac.readEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8");
        if (fac.get_LastMethodSuccess() != true) {
            strOut.append(fac.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

        CkAuthGoogle gAuth;
        gAuth.put_JsonKey(jsonKey);
        gAuth.put_Scope("https://www.googleapis.com/auth/cloud-platform");
        gAuth.put_ExpireNumSeconds(3600);
        gAuth.put_SubEmailAddress("");

        CkSocket tlsSock;
        success = tlsSock.Connect("www.googleapis.com",443,true,5000);
        if (success != true) {
            strOut.append(tlsSock.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

        success = gAuth.ObtainAccessToken(tlsSock);
        if (success != true) {
            strOut.append(gAuth.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

        fac.WriteEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt",gAuth.accessToken(),"utf-8",false);

        // Retry the original request.
        http.put_AuthToken(gAuth.accessToken());
        success = http.DownloadBd(url,fileData);
        if (success == false) {
            strOut.append(http.lastErrorText());
            strOut.append("\r\n");
            SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
            return;
        }

    }

    if (responseCode != 200) {
        // Get the error response
        CkStringBuilder sbErrorResponse;
        sbErrorResponse.AppendBd(fileData,"utf-8",0,0);
        strOut.append("Error response code = ");
        strOut.appendInt(responseCode);
        strOut.append("\r\n");
        strOut.append("Error:");
        strOut.append("\r\n");
        strOut.append(sbErrorResponse.getAsString());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    strOut.append("Success.");
    strOut.append("\r\n");

    // Save the downloaded data to a file.
    success = fileData.WriteFile("qa_output/starfish.jpg");


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }