Check expiration of Jwt token in ASP.Net Core

I have JWT code below:

private string CreateJWT(User user)
{
    var secretKey = configuration.GetSection("AppSettings:Key").Value;
    var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(secretKey));
 
    var claims = new Claim[] {
        new Claim(ClaimTypes.Name, user.Username),
        new Claim(ClaimTypes.NameIdentifier, user.Id.ToString())
    };
 
    var signingCredentials = new SigningCredentials(
                            key, SecurityAlgorithms.HmacSha256Signature);
 
    var tokenDescriptor = new SecurityTokenDescriptor{
        Subject = new ClaimsIdentity(claims),
        Expires = DateTime.UtcNow.AddMinutes(20),
        SigningCredentials = signingCredentials
    };
 
    var tokenHandler = new JwtSecurityTokenHandler();
    var token = tokenHandler.CreateToken(tokenDescriptor);
    return tokenHandler.WriteToken(token);
}

and I see this line of code:

Expires = DateTime.UtcNow.AddMinutes(20),

I know that if i stay in the page for that long and tried to browse it will give me unauthorized message. I want the app to check that the token is expired and logout the user authomatically.