How to get "exp" from jwt token and compare with it current time to check if token is expired

Question

I am using System.IdentityModel.Tokens.Jwt package and the below code decoding the jwt token, but it won't give exp value?

 var handler = new JwtSecurityTokenHandler();
 var decodedValue = handler.ReadJwtToken("token");

How to get exp and compare it with the current DateTime to calculate token is expired or not?

Update:

I am using Azure.Core.AccessToken where I have the below property,

public DateTimeOffset ExpiresOn
    {
        get;
    }

Alexander

Do you mean that for the token in question, the ValidTo field isn't returning a valid DateTime representative of the expiry? If not, can you clarify your question, please? – Cloraclorinda

Please check the answer here: #39926604 – Norty

@Llama, there is one property ExpiresOn coming as part of access token, how to compare this DateTimeOffset with current date? – Alexander

I'm not seeing ExpiresOn in JwtSecurityToken's docs (here), though it does state that ValidTo represents the exp claim. Where are you seeing the ExpiresOn property? – Cloraclorinda

Wait, are you just asking for something like if (token.ExpiresOn > DateTimeOffset.UtcNow) or something? – Cloraclorinda

@Llama, I have azure ad token which generates through azure managed identity and looks like it's different than jwt token. it's a Azure.Core.AccessToken token – Alexander

@Llama, I got my answer. if (token.ExpiresOn > DateTimeOffset.UtcNow). Thanks! – Alexander

I guess this answers your question then. – Cloraclorinda

Answer 1

This is how I check if a token is valid.

using System.IdentityModel.Tokens.Jwt;

private bool IsValid(string token)
{
    JwtSecurityToken jwtSecurityToken;
    try
    {
        jwtSecurityToken = new JwtSecurityToken(token);
    }
    catch (Exception)
    {
        return false;
    }
    
    return jwtSecurityToken.ValidTo > DateTime.UtcNow;
}

Heroic

This is still not valid for me on IIS Express Win 10 VS2019 .NET Core 5. I am on GMT+7 – Pattison

Oh, maybe this is correct too. because, at my localhost, this code is working fine. But when at development server, the release process maybe not working. I will re-check at another project. I will try to use this and another one use first answer. – Pattison

I'm on GMT+3 but have no problems with this code. – Heroic

Answer 2

I use this:

using System.IdentityModel.Tokens.Jwt;

public static long GetTokenExpirationTime(string token)
    {
        var handler = new JwtSecurityTokenHandler();
        var jwtSecurityToken = handler.ReadJwtToken(token);
        var tokenExp = jwtSecurityToken.Claims.First(claim => claim.Type.Equals("exp")).Value;
        var ticks= long.Parse(tokenExp);
        return ticks;
    }

public static bool CheckTokenIsValid(string token)
    {
        var tokenTicks = GetTokenExpirationTime(token);
        var tokenDate = DateTimeOffset.FromUnixTimeSeconds(tokenTicks).UtcDateTime;

        var now = DateTime.Now.ToUniversalTime();

        var valid = tokenDate >= now;

        return valid;
    }

Lair

System.Linq is required to use the First method of the Claims IEnumerator. Add using System.Linq; at the top. – Enate

Why not use var now = DateTime.UtcNow; instead of var now = DateTime.Now.ToUniversalTime(); ? – Scanties

I was just testing other ways... – Lair

This is correct way for me.. – Pattison

Answer 3

Glad that you found your solution Posting the complete answer for helping community member when they will encounter the same problem.

For Reproducing the issue, I have generated an Access token using Ouath2.0 with client credential with shared secret.

C# Code for converting Unix timestamps into DateTimes

using System;

public class HelloWorld
{
    
    public static DateTime ConvertFromUnixTimestamp(int timestamp)
{
    DateTime origin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
    return origin.AddSeconds(timestamp); //
}
    
    public static void Main(string[] args)
    {
        Console.WriteLine ("Hello Mono World");
        int timestamp=1643438945;
        DateTime date=ConvertFromUnixTimestamp(timestamp);
        Console.WriteLine("Token Expire time "+date);
        if (date>DateTimeOffset.UtcNow)
        {
            Console.WriteLine ("Token is not expire");
        }
        else {
            Console.WriteLine ("Token has expired");
        }
    }
}

Output--

Boer

hello @RahulKumarShaw-MT... my question mainly around, how to decode the jwt token and get the exp value out of it in C#, 2nd part is compare where you're solution works for me. But I got answer like this if (token.ExpiresOn > DateTimeOffset.UtcNow). Thanks for your answer and appreciate! – Alexander