Below, I’ll describe a simple way to read the header and extract an information.
Logic
Which usings
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using System;
using System.Collections.Generic;
using System.IdentityModel.Tokens.Jwt;
using System.Linq;
using System.Text;
using Microsoft.AspNetCore.Http;
using Microsoft.IdentityModel.Tokens;
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This is the first step. The header used to pass the JWT value is Authorization:
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public static string GetJwtTokenFromRequest(HttpContext context)
{
var authHeader = context.Request.Headers["Authorization"].FirstOrDefault();
if (string.IsNullOrEmpty(authHeader))
{
//no authorization header
return null;
}
if (!authHeader.StartsWith("Bearer "))
{
//no bearer but authorization header returned
return authHeader;
}
//bearer present, returning trimmed value
return authHeader.Substring("Bearer ".Length).Trim();
}
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The code above actually takes care of the presence of Bearer in the header value.
It is best practice to use it (at least, I’ve never seen passing or receiving the Authorization without Bearer)
Decode the JWT value
Let’s dive into the decoding.
The code below actually validates the siging key (see ValidateIssuerSigningKey).
To validate other parts, visit the Microsoft website.
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public static string GetInformationFromToken(HttpContext context, string dataProp)
{
var token = GetJwtTokenFromRequest(context);
if (string.IsNullOrEmpty(token))
{
//token is empty, returning null
return null;
}
try
{
var tokenHandler = new JwtSecurityTokenHandler();
tokenHandler.ValidateToken(token, new TokenValidationParameters
{
ValidateIssuerSigningKey = true,
ValidateIssuer = false,
ValidateAudience = false
}, out SecurityToken validatedToken);
var jwtToken = (JwtSecurityToken)validatedToken;
//the JwtSecurityToken contains a property "Claims" from which you extract a data property that you want to read
var targetInfo = jwtToken.Claims.FirstOrDefault(c => c.Type == dataProp);
if (targetInfo != null)
{
return targetInfo.Value;
}
return null;
}
catch (Exception e)
{
// Token validation failed
return null;
}
}
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Usage
Then, you simply call like so:
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var dataExtractedFromJwt =
JwtTokenHelper.GetInformationFromToken(
HttpContextAccessor.HttpContext,
"some_data_in_jwt");
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Credit: Photo by Markus Spiske on Unsplash.
