2-legged CkOAuth2

2-legged OAuth2 is a name for the following general sequence of events:

1. The app sends an HTTP request with a secret of some sort, and the server responds with an access token.
2. The access token is used as the credential in the web API requests.

The exact specifics of these 2 steps can vary. When you want to implement 2-legged OAuth2, you don't necessarily look for a "2-legged OAuth2 implementation". You want to instead look at the specifics of the steps and then solve each of those smaller problems. In this case, it's easy.

In this case, Step 1 is this:

Authorization Request:

POST /oauth/token HTTP/1.1
Authorization: ** HTTP basic authentication with client_id and client_secret **
Content-Type: application/x-www-form-urlencoded; charset=utf-8
Host: auth.weather.mg
Connection: close
grant_type=client_credentials
Authorization Response:
HTTP/1.1 200
Cache-Control: no-store
Pragma: no-cache
Content-Type: application/json;charset=UTF-8
Connection: close
{
    "access_token": "JWT_ACCESS_TOKEN",
    "token_type": "bearer",
    "expires_in": 3600,
    "scope": "space separated list of allowed scopes",
    "domain": "meteogroup",
    "jti": "id of JWT_ACCESS_TOKEN"
}

So this is easy. It's just a matter of sending a POST with Basic Authentication with a URL encoded parameter in the body of the POST. Using Chilkat's CkHttp class, this is what you do (in pseudo-code, applicable in any supported programming language where the syntax and naming might be different)

Http http;
http.Login = "myUsername";
http.Password = "myPassword";
http.BasicAuth = true;
HttpRequest req;
req.AddParam("grant_type","client_credentials");
HttpResponse resp = http.PostUrlEncoded("https://auth.weather.mg//oauth/token",req);
string jsonResponse = resp.BodyStr;

Now you have the JSON response and you can parse out the access token and other fields using Chilkat's JsonObject class or any other JSON API.

Step 2 is to send the access token in an Authorization header in web API requests:

GET /observation?location=53,13 HTTP/1.1
Authorization: Bearer JWT_ACCESS_TOKEN
Host: api.weather.mg
Connection: close

If using Chilkat Http, just set the http.AuthToken property equal to the JWT_ACCESS_TOKEN. This adds the "Authorization: Bearer JWT_ACCESS_TOKEN" header field to the request header. That's all..