ASP.NET Web API Media-Type Formatter for Gravatar

Customer.cs

    public class Customer
    {       
        public string FirstName { get; set; }        
        public string LastName { get; set; }
        public String Email { get; set; }
    }

GravatarFormatter.cs

  public class GravatarFormatter : MediaTypeFormatter
    {
        private const string GRAVATAR_TEMPLATE = "https://www.gravatar.com/avatar/{0}";

        public GravatarFormatter()
        {
            SupportedMediaTypes.Add(new MediaTypeHeaderValue("image/png"));
        }

        public override bool CanReadType(Type type)
        {
            return false;
        }

        public override bool CanWriteType(Type type)
        {
            return type == typeof(Customer);
        }

        public override async Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
        {
            var customer = value as Customer;
            if (customer != null)
            {
                var email = customer.Email;
                string hashedEmail = string.Empty;

                using (var md5haser = MD5.Create())
                {
                    var byteHash = md5haser.ComputeHash(Encoding.UTF8.GetBytes(email));

                    var builder = new StringBuilder();
                    for (int i = 0; i < byteHash.Length; i++)
                    {
                        builder.Append(byteHash[i].ToString("x2"));
                    }
                    hashedEmail = builder.ToString();
                }
                var gravatarUrl = string.Format(GRAVATAR_TEMPLATE, hashedEmail);

                var client = new HttpClient();

                var responseBytes = await client.GetByteArrayAsync(gravatarUrl);
                await writeStream.WriteAsync(responseBytes, 0, responseBytes.Length);
            }
        }
    }