(C# UWP/WinRT) 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 Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

// 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..
Chilkat.StringBuilder sbToken = new Chilkat.StringBuilder();
bool success = sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8");
if (success == false) {
    Debug.WriteLine("Failed to load access token.");
    return;
}

Chilkat.Http http = new Chilkat.Http();

http.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");
string 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..
Chilkat.BinData fileData = new Chilkat.BinData();
success = await http.DownloadBdAsync(url,fileData);
int responseCode = http.LastStatus;
if ((success == false) && (responseCode != 401)) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

if (responseCode == 401) {
    Debug.WriteLine("Received 401 Unauthorized response. Attempting to refresh the access token...");

    // May be that the access token expired.
    // Load our JSON key and request a new access token, then retry the original request.
    Chilkat.FileAccess fac = new Chilkat.FileAccess();
    string jsonKey = fac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8");
    if (fac.LastMethodSuccess != true) {
        Debug.WriteLine(fac.LastErrorText);
        return;
    }

    Chilkat.AuthGoogle gAuth = new Chilkat.AuthGoogle();
    gAuth.JsonKey = jsonKey;
    gAuth.Scope = "https://www.googleapis.com/auth/cloud-platform";
    gAuth.ExpireNumSeconds = 3600;
    gAuth.SubEmailAddress = "";

    Chilkat.Socket tlsSock = new Chilkat.Socket();
    success = await tlsSock.ConnectAsync("www.googleapis.com",443,true,5000);
    if (success != true) {
        Debug.WriteLine(tlsSock.LastErrorText);
        return;
    }

    success = await gAuth.ObtainAccessTokenAsync(tlsSock);
    if (success != true) {
        Debug.WriteLine(gAuth.LastErrorText);
        return;
    }

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

    // Retry the original request.
    http.AuthToken = gAuth.AccessToken;
    success = await http.DownloadBdAsync(url,fileData);
    if (success == false) {
        Debug.WriteLine(http.LastErrorText);
        return;
    }

}

if (responseCode != 200) {
    // Get the error response
    Chilkat.StringBuilder sbErrorResponse = new Chilkat.StringBuilder();
    sbErrorResponse.AppendBd(fileData,"utf-8",0,0);
    Debug.WriteLine("Error response code = " + Convert.ToString(responseCode));
    Debug.WriteLine("Error:");
    Debug.WriteLine(sbErrorResponse.GetAsString());
    return;
}

Debug.WriteLine("Success.");

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