How to decode JWT token by C#?

Question

I am using .NET 5, ASP.NET Core 5 Web API and ASP.NET Core Identity. I have a JWT token:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJFbWFpbCI6ImR1Y3R4QG1wc29sdXRpb25zLmlvIiwiaHR0cDovL3NjaGVtYXMueG1sc29hcC5vcmcvd3MvMjAwNS8wNS9pZGVudGl0eS9jbGFpbXMvbmFtZWlkZW50aWZpZXIiOiJiM2E2ZTI5Zi1hZjdjLTRhZmUtYjA4Ni1jYmVjMjAzOTYxYmUiLCJleHAiOjE2MDE4ODk4OTksImlzcyI6Imh0dHA6Ly9tcHNvbHV0aW9ucy5pbyIsImF1ZCI6Imh0dHA6Ly9tcHNvbHV0aW9ucy5pbyJ9.0HmUptS8_VMPuYXMlSwfafhusiYPfyOPPaiSo6uSOMs

I need to get email string foo@example.com. How to decode JWT token, then get email string in C#?

Answer 1

This shows how to decode & retrieve info from a Json Web Token, you may need to install nuget :- System.IdentityModel.Tokens.Jwt

using System.IdentityModel.Tokens.Jwt;

// A jwt encoded token string in this case extracted from the 'Authorization' HTTP header
var tokenString = "Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsIng1dCI6Ik1uQ19WWmNBVGZNNXBPWWlKSE1iYTlnb0VLWSJ9.eyJhdWQiOiIwMDAwMDAwMC0wMDAwLTAwMDAtMDAwMC0wMDAwMDAwMDAwMDAiLCJpc3MiOiJodHRwczovL3N0cy53aW5kb3dzLm5ldC8wMDAwMDAwMC0wMDAwLTAwMDAtMDAwMC0wMDAwMDAwMDAwMDAiLCJpYXQiOiIxNDI4MDM2NTM5IiwibmJmIjoiMTQyODAzNjUzOSIsImV4cCI6IjE0MjgwNDA0MzkiLCJ2ZXIiOiIxLjAiLCJ0aWQiOiIwMDAwMDAwMC0wMDAwLTAwMDAtMDAwMC0wMDAwMDAwMDAwMDAiLCJhbXIiOiJwd2QiLCJvaWQiOiIwMDAwMDAwMC0wMDAwLTAwMDAtMDAwMC0wMDAwMDAwMDAwMDAiLCJlbWFpbCI6Impkb2VAbGl2ZS5jb20iLCJwdWlkIjoiSm9obiBEb2UiLCJpZHAiOiJsaXZlLmNvbSIsImFsdHNlY2lkIjoiMTpsaXZlLmNvbTowMDAwMDAwMDAwMDAwMDAwIiwic3ViIjoieHh4eHh4eHh4eHh4eHh4eC15eXl5eSIsImdpdmVuX25hbWUiOiJKb2huIiwiZmFtaWx5X25hbWUiOiJEb2UiLCJuYW1lIjoiSm9obiBEb2UiLCJncm91cHMiOiIwMDAwMDAwMC0wMDAwLTAwMDAtMDAwMC0wMDAwMDAwMDAwMDAiLCJ1bmlxdWVfbmFtZSI6ImxpdmUuY29tI2pkb2VAbGl2ZS5jb20iLCJhcHBpZCI6IjAwMDAwMDAwLTAwMDAtMDAwMC0wMDAwLTAwMDAwMDAwMDAwMCIsImFwcGlkYWNyIjoiMCIsInNjcCI6InVzZXJfaW1wZXJzb25hdGlvbiIsImFjciI6IjEifQ.K7BCa0NO-A5f9exFiWcIXFMGnLmmt3V2HVP0itMT-GsAxnQROWzJFDIQNFo4QhiW0NCCqJykVELeVBCy_7Dex2-szUPZ69rmmDVJhy_qkmAiHhS1mNZDvJ1sB-whb5wOJ_QPIlByVzubhTcNnuliTVjnTeuOurVJJcn0Vugx9UDkGgky0etHXzmKukWYp4nzA68Wf1xnzlMZBz7PfoPGhjgzQfceOkZJVXIBRMB_7tsyW7gYNbHB_aTiT47cEjkh-UdrZEdp2UaAKugC-es3m076kRHMJqx31x-zDLDBttKinRJVPctiqwb1jMOMV6cUAp2E6aMfEbNk_iqX_OKFJg";  

// Trim 'Bearer ' from the start since its just a prefix for the token
var jwtEncodedString = tokenString.Substring(7);

// Instantiate a new Jwt Security Token from the Jwt Encoded String
var token = new JwtSecurityToken(jwtEncodedString);

// Retrieve info from the Json Web Token 
Console.WriteLine("email => " + token.Claims.First(c => c.Type == "Email").Value);

Ref: https://gist.github.com/ptsurbeleu/4aa7851e2d8eaffec488