private List<Claim> ValidateToken(string token, string nonce)
        {
            var certString = "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";
            var cert = new X509Certificate2(Convert.FromBase64String(certString));

            var parameters = new TokenValidationParameters
            {
                ValidAudience = "codeclient",
                ValidIssuer = Constants.BaseAddress,
                IssuerSigningToken = new X509SecurityToken(cert)
            };

            SecurityToken jwt;
            var principal = new JwtSecurityTokenHandler().ValidateToken(token, parameters, out jwt);

            // validate nonce
            var nonceClaim = principal.FindFirst("nonce");

            if (!string.Equals(nonceClaim.Value, nonce, StringComparison.Ordinal))
            {
                throw new Exception("invalid nonce");
            }

            return principal.Claims.ToList();
        }