How to extract and get a claim from token?

Question

I've been looking for an exact answer but it seems most answers are client call and out of the scope.

Question: I already have an access token access token. How to get a claim using c# code given an access token ONLY?

I think: Below are the same questions but no answers i think fits.

How to get the claims out of a authenticated SecurityToken

How do I read claims from my Oauth token?

Answer 1

Install-Package Newtonsoft.Json

The access token is just base64 encoded JSON. You can parse the token as follows

        string token =
            "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ";
        var parts = token.Split('.');
        var decoded = Convert.FromBase64String(parts[1]);
        var part = Encoding.UTF8.GetString(decoded);
        var jwt = JObject.Parse(part);
        var name = jwt["name"].Value<string>();

UPDATE

1. Parsing access token on the client is not recommended, access token should be parsed only on the resource server.
2. You must validate the access token on the resource server to make sure that token has not tampered on the way.

3. Most of the time you dont need to parse token as above, Just use a recommended JWT library that does both validation and parsing. e.g.

   app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());