(Mono C#) Auth0 Server-to-Server Access Token (Client Credentials flow)

Demonstrates how to obtain an Auth0 access token using client credentials (client_id and client_secret).

This is just a matter of duplicating this CURL command:

curl --request POST
  --url 'https://chilkat.auth0.com/oauth/token' \
  --header 'content-type: application/json' \
  --data '{"grant_type":"client_credentials","client_id": "xxxx","client_secret": "xxxx","audience": "https://api.example.com/geocoding/v1/"}'

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

// We want to duplicate this curl command:
// 
// curl --request POST
//   --url 'https://chilkat.auth0.com/oauth/token' \
//   --header 'content-type: application/json' \
//   --data '{"grant_type":"client_credentials","client_id": "my_client_id","client_secret": "my_client_secret","audience": "https://api.example.com/geocoding/v1/"}'

// Build the JSON body of the request.
Chilkat.JsonObject json = new Chilkat.JsonObject();
json.UpdateString("grant_type","client_credentials");
json.UpdateString("client_id","AUTH0-CLIENT-ID");
json.UpdateString("client_secret","AUTH0-CLIENT-SECRET");
json.UpdateString("audience","https://api.example.com/geocoding/v1/");

// IMPORTANT: You would use your own url.  You would not use "chilkat.auth0.com".  
// Instead you would use "your_name.auth0.com"
Chilkat.Http http = new Chilkat.Http();
Chilkat.HttpResponse resp = http.PostJson3("https://chilkat.auth0.com/oauth/token","application/json",json);
if (http.LastMethodSuccess != true) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

// A 200 response status code indicates success.  In the success case, the response body
// contains the JSON access token, such as: 
// {
//   "access_token": "eyJz93a...k4laUWw",
//   "token_type":"Bearer",
//   "expires_in":86400
// }
// 

Debug.WriteLine("response status code = " + Convert.ToString(resp.StatusCode));

// The repsonse is JSON if successful and also JSON for errors.
Chilkat.JsonObject jsonResp = new Chilkat.JsonObject();
jsonResp.EmitCompact = false;
jsonResp.Load(resp.BodyStr);

if (resp.StatusCode != 200) {
    // The response body contains error information in JSON format.
    Debug.WriteLine(jsonResp.Emit());

    // An example of an error response:
    // 		{
    // 		  "error": "access_denied",
    // 		  "error_description": "Client is not authorized to access \"https://api.example.com/geocoding/v1/\". You might probably want to create a \"client-grant\" associated to this API. See: https://auth0.com/docs/api/v2#!/Client_Grants/post_client_grants"
    // 		}
    return;
}

Debug.WriteLine("Success!");
Debug.WriteLine(jsonResp.Emit());

// A successful JSON response body looks like this:

// {
//   "access_token": "eyJz93a...k4laUWw",
//   "token_type":"Bearer",
//   "expires_in":86400
// }