IDX10503: Signature validation failed. Token does not have a kid. Keys tried: 'System.Text.StringBuilder'

Question

I have the below JWT token,

eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJjbGllbnRpZCIsImF1ZCI6ImNsaWVudGlkIiwic3ViIjoiMTIzIiwiYSI6IjQ1NiIsImlhdCI6MTYyMTc5OTU5OCwiZXhwIjoxNjIxNzk5NjU4fQ.hglbX63zhPwTOsB-zSiOMfxEKl5OaIk6zX1o9-LEhP3nro8fa5_3QyIH7I5971j-xuO1bccX1TOh0kNcQ-ACAg

Which is generated using,

    public static string GenerateToken(string key, string a1, string a2)
    {
        var securityKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(key));
        var token = new JwtSecurityToken(
            claims: new Claim[]
            {
            new Claim(JwtRegisteredClaimNames.Iss, "clientid"),
            new Claim(JwtRegisteredClaimNames.Aud, "clientid"),
            new Claim(JwtRegisteredClaimNames.Sub, a1),
            new Claim("a", a2),
            new Claim(JwtRegisteredClaimNames.Iat, DateTimeOffset.UtcNow.ToUnixTimeSeconds().ToString(), ClaimValueTypes.Integer64),
            },
            //notBefore: new DateTimeOffset(DateTime.Now).DateTime,
            expires: new DateTimeOffset(DateTime.Now.AddMinutes(1)).DateTime,
            signingCredentials: new SigningCredentials(securityKey, SecurityAlgorithms.HmacSha512)
        );

        return new JwtSecurityTokenHandler().WriteToken(token);
    }

var key = "Ym7AD3OT2kpuIRcVAXCweYhV64B0Oi9ETAO6XRbqB8LDL3tF4bMk9x/59PljcGbP5v38BSzCjD1VTwuO6iWA8uzDVAjw2fMNfcT2/LyRlMOsynblo3envlivtgHnKkZj6HqRrG5ltgwy5NsCQ7WwwYPkldhLTF+wUYAnq28+QnU=";
// Key is test                
var token = GenerateToken(key, "123", "456");

After getting token I am validating using below code,

var key = "Ym7AD3OT2kpuIRcVAXCweYhV64B0Oi9ETAO6XRbqB8LDL3tF4bMk9x/59PljcGbP5v38BSzCjD1VTwuO6iWA8uzDVAjw2fMNfcT2/LyRlMOsynblo3envlivtgHnKkZj6HqRrG5ltgwy5NsCQ7WwwYPkldhLTF+wUYAnq28+QnU=";
// key is test

var hmac = new HMACSHA512(Convert.FromBase64String(key));
var validationParameters = new TokenValidationParameters
            {
                ValidAudience = "clientid",
                ValidIssuer = "clientid",
                IssuerSigningKey = new SymmetricSecurityKey(hmac.Key)
            };
            var tokenHandler = new JwtSecurityTokenHandler();
            return tokenHandler.ValidateToken(token, validationParameters, out var validToken);

But I am getting below error,

IDX10503: Signature validation failed. Token does not have a kid. Keys tried: 'System.Text.StringBuilder'.
Exceptions caught:
 'System.Text.StringBuilder'.
token: 'System.IdentityModel.Tokens.Jwt.JwtSecurityToken'.

Answer 1

The issue was this line,

var hmac = new HMACSHA512(Convert.FromBase64String(key));

I changed it to,

var hmac = new HMACSHA512(Encoding.UTF8.GetBytes(key));

The error is misleading. Soure code for the error is at https://github.com/AzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet/blob/d6f2b66d788195b50f2b1f700beb497851194c73/src/System.IdentityModel.Tokens.Jwt/JwtSecurityTokenHandler.cs#L1016