(.NET Core C#) Refresh GMail IMAP OAuth2 Access Token

Demonstrates how to refresh an access token GMail IMAP read/write access.

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

// See Get GMail IMAP OAuth2 Access Token for Desktop App 
// for sample code showing how to obtain a GMail IMAP read/write access token.

// It is assumed we previously obtained an OAuth2 access token for GMail.

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

// The access token JSON looks something like this:

// 	{ 
// 	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
// 	 "token_type": "Bearer",
// 	 "expires_in": 3600,
// 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
// 	}
// 

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

oauth2.TokenEndpoint = "https://www.googleapis.com/oauth2/v4/token";

// Replace these with actual values.
oauth2.ClientId = "GOOGLE-CLIENT-ID";
oauth2.ClientSecret = "GOOGLE-CLIENT-SECRET";

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

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

Debug.WriteLine("New access token: " + oauth2.AccessToken);

// The response contains a new access token, but we must keep
// our existing refresh token for when we need to refresh again in the future.
jsonToken.UpdateString("access_token",oauth2.AccessToken);

// 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/_gmailFullAccess.json","utf-8",false);

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