(.NET Core C#) Refresh a Constant Contact OAuth2 Access Token

Refreshes a Constant Contact OAuth2 access token. When an access token expires, HTTPS requests will receive a 401 status response indicating failure. When that happens, your application can run this code to refresh the access token, and then retry the request using the new access token. Refreshing an access token does not need user interaction (i.e. does not need to display a browser to have the user interactive authorize access).

For more information, see https://v3.developer.constantcontact.com/api_guide/server_flow.html#step-5-refresh-the-access-token

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

// It is assumed we previously obtained an OAuth2 access token.
// This example loads the JSON access token file 
// saved by this example: Get Constant Contact OAuth2 Access Token

Chilkat.JsonObject jsonToken = new Chilkat.JsonObject();
bool success = jsonToken.LoadFile("qa_data/tokens/constantContact.json");
if (success != true) {
    Debug.WriteLine("Failed to load constantContact.json");
    return;
}

// The access token JSON looks like this:

// {
//   "access_token": "aEr4czHReESHUGcc2LRknzsMxUbW",
//   "refresh_token": "s2qH27ikM7r3Ia0LrZGDOIgKw0bubUotBdJ7fTtc7y",
//   "token_type": "Bearer"
// }

Chilkat.OAuth2 oauth2 = new Chilkat.OAuth2();

oauth2.VerboseLogging = true;

oauth2.TokenEndpoint = "https://idfed.constantcontact.com/as/token.oauth2";
oauth2.UseBasicAuth = true;
oauth2.UncommonOptions = "OAUTH2_REFRESH_NO_SCOPE";

// Replace these with actual values.
oauth2.ClientId = "CLIENT_KEY";
oauth2.ClientSecret = "CLIENT_SECRET";

// Get the "refresh_token"
oauth2.RefreshToken = jsonToken.StringOf("refresh_token");

Debug.WriteLine("Existing refresh_token: " + oauth2.RefreshToken);

// Send the HTTP POST to refresh the access token..
success = oauth2.RefreshAccessToken();
if (success != true) {
    Debug.WriteLine(oauth2.LastErrorText);
    return;
}

jsonToken.UpdateString("access_token",oauth2.AccessToken);
jsonToken.UpdateString("refresh_token",oauth2.RefreshToken);

// Save the new JSON access token response to a file.
Chilkat.StringBuilder sbJson = new Chilkat.StringBuilder();
jsonToken.EmitCompact = false;
jsonToken.EmitSb(sbJson);
sbJson.WriteFile("qa_data/tokens/constantContact.json","utf-8",false);

Debug.WriteLine("OAuth2 token refreshed!");
Debug.WriteLine("New Access Token = " + oauth2.AccessToken);
Debug.WriteLine("New refresh_token: " + oauth2.RefreshToken);