Base64 decode a JWT in C# .NET Core

base64-decode-jwt.cs

// Add the following nuget package for Base64Url decoding:
// dotnet add package Microsoft.AspNetCore.WebUtilities

// This example JWT is taken from jwt.io
string jwt = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c";
string[] parts = jwt.Split('.');

foreach (string section in parts)
{
 	// The final (3rd) section is the JWT signature, so will appear as nonsense as it isn't JSON
	byte[] bytes = WebEncoders.Base64UrlDecode(section);
	string json = System.Text.Encoding.UTF8.GetString(bytes);
  
 	Console.WriteLine(json);
}

// Output:
//
// {"alg":"HS256","typ":"JWT"}
// {"sub":"1234567890","name":"John Doe","iat":1516239022}
// I�J�04IHNJ(]�O��lj~�:N�%_�u0B,×
//