JWT Unable to decode the header as Base64Url encoded string

Question

I have the following code:

public async Task<LoginResult> GenerateJwtTokenAsync(string email, string password)
{
    LoginResult loginResult = await _membershipProvider.Login(email, password);
    if (loginResult.Succeeded)
    {
        var symmetricKey = Convert.FromBase64String(Secret);

        var tokenDescriptor = new SecurityTokenDescriptor
        {
            Subject = new ClaimsIdentity(loginResult.Claims),
            Expires = DateTime.UtcNow.AddDays(1),
            SigningCredentials = new SigningCredentials(new SymmetricSecurityKey(symmetricKey), SecurityAlgorithms.HmacSha256Signature)
        };

        var stoken = _tokenHandler.CreateToken(tokenDescriptor);
        var token = _tokenHandler.WriteToken(stoken);

        // Check token here to see if it works
        var jwtToken = _tokenHandler.ReadToken(token) as JwtSecurityToken;
        loginResult.JwtToken = token;
    }
    return loginResult;
}

public ClaimsPrincipal ValidateJwtToken(string tokenString)
{

    ClaimsPrincipal principal;

    try
    {
        var jwtToken = _tokenHandler.ReadToken(tokenString) as JwtSecurityToken;

        if (jwtToken == null)
        {
            principal = null;
        }
        else
        {
            var symmetricKey = Convert.FromBase64String(Secret);

            var validationParameters = new TokenValidationParameters()
            {
                RequireExpirationTime = true,
                ValidateIssuer = false,
                ValidateAudience = false,
                IssuerSigningKey = new SymmetricSecurityKey(symmetricKey)
            };

            SecurityToken securityToken;
            principal = _tokenHandler.ValidateToken(tokenString, validationParameters, out securityToken);
        }
    }
    catch (Exception ex)
    {
        principal = null;
    }

    return principal;
}

The line below reads the token perfectly, however when I actually read it in the 2nd method I get an exception.

// Check token here to see if it works
var jwtToken = _tokenHandler.ReadToken(token) as JwtSecurityToken

I have verified the two string are identical, I am extremely confused as to why this stops working when I actually want to validate the token for the life of me I can't see what I am doing wrong. Any ideas please?

EDIT:

Exception

   "IDX10729: Unable to decode the header 'header' as Base64Url encoded string. jwtEncodedString: 'Token here'."

Stack trace:

   at System.IdentityModel.Tokens.Jwt.JwtSecurityToken.Decode(String[] tokenParts, String rawData)
   at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.ReadJwtToken(String token)
   at AuthService.ValidateJwtToken(String tokenString) in AuthService.cs:line 57

Answer 1

I was having this error and found, by observing the error detail, that the cause was that Newtonsoft.Json dll was not loaded.

The System.IdentityModel.Tokens.Jwt.JsonExtensions was trying to load version 9.0.0.0 of the dll but the project was using version 10.0.0.0. The error detail have something like this:

System.ArgumentException: IDX10729: ... Could not load file or assembly 'Newtonsoft.Json, Version=9.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed' or one of its dependencies

I resolved by adding this binding to the config:

 <runtime>
    <assemblyBinding  xmlns="urn:schemas-microsoft-com:asm.v1">
       <dependentAssembly>
        <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-10.0.0.0" newVersion="10.0.0.0" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>

Answer 2

I was getting the same error validating the token. I solved adding the Newtonsoft.Json dll to the project.