Done it though I'm not certain this is the best way so if anyone knows better please let me know.

https://www.tanasuk.com/blog/Get%20users%20email%20from%20Twitter%20API

        app.UseTwitterAuthentication(new Microsoft.Owin.Security.Twitter.TwitterAuthenticationOptions() {
              ConsumerKey = consumerKey,
              ConsumerSecret = consumerSecret, 
              CallbackPath = new PathString("/umbraco/surface/UmbracoIdentityAccount/ExternalLoginConfirmation"),
                Provider = new TwitterAuthenticationProvider
                {
                    OnAuthenticated = context =>
                    {
                        TwitterDto response = oauthLogin(context.AccessToken, context.AccessTokenSecret,  consumerKey, consumerSecret);
                        context.Identity.AddClaim(new System.Security.Claims.Claim("urn:twitter:access_token",context.AccessToken ));
                        context.Identity.AddClaim(new System.Security.Claims.Claim("urn:twitter:access_secret", context.AccessTokenSecret));
                        context.Identity.AddClaim(new System.Security.Claims.Claim(ClaimTypes.Email, response.email));
                        return Task.CompletedTask;
                    },
                    OnReturnEndpoint = (context) =>
                    {
                        return Task.CompletedTask;
                    }
                }
        });


    public static TwitterDto oauthLogin(string oauth_token, string oauth_token_secret, string oauth_consumer_key, string oauth_consumer_secret)
    {
        // oauth implementation details
        var oauth_version = "1.0";
        var oauth_signature_method = "HMAC-SHA1";

        // unique request details
        var oauth_nonce = Convert.ToBase64String(new ASCIIEncoding().GetBytes(DateTime.Now.Ticks.ToString()));
        var nowUtc = DateTime.UtcNow;
        var timeSpan = nowUtc - new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
        var oauth_timestamp = Convert.ToInt64(timeSpan.TotalSeconds).ToString();

        var resource_url = "https://api.twitter.com/1.1/account/verify_credentials.json";
        var request_query = "include_email=true";
        // create oauth signature
        var baseFormat = "oauth_consumer_key={0}&oauth_nonce={1}&oauth_signature_method={2}" +
                        "&oauth_timestamp={3}&oauth_token={4}&oauth_version={5}";

        var baseString = string.Format(baseFormat,
                                    oauth_consumer_key,
                                    oauth_nonce,
                                    oauth_signature_method,
                                    oauth_timestamp,
                                    oauth_token,
                                    oauth_version
                                    );

        baseString = string.Concat("GET&", Uri.EscapeDataString(resource_url) + "&" + Uri.EscapeDataString(request_query), "%26", Uri.EscapeDataString(baseString));

        var compositeKey = string.Concat(Uri.EscapeDataString(oauth_consumer_secret),
                                "&", Uri.EscapeDataString(oauth_token_secret));


        string oauth_signature;
        using (var hasher = new HMACSHA1(Encoding.ASCII.GetBytes(compositeKey)))
        {
            oauth_signature = Convert.ToBase64String(
                hasher.ComputeHash(Encoding.ASCII.GetBytes(baseString)));
        }

        const string headerFormat = "OAuth oauth_nonce=\"{0}\",oauth_signature_method =\"{1}\", " +
                                     "oauth_timestamp=\"{2}\",oauth_consumer_key =\"{3}\", " +
                                     "oauth_token=\"{4}\",oauth_signature =\"{5}\", " +
                                     "oauth_version=\"{6}\"";

        var authHeader = string.Format(headerFormat,
                                       Uri.EscapeDataString(oauth_nonce),
                                       Uri.EscapeDataString(oauth_signature_method),
                                       Uri.EscapeDataString(oauth_timestamp),
                                       Uri.EscapeDataString(oauth_consumer_key),
                                       Uri.EscapeDataString(oauth_token),
                                       Uri.EscapeDataString(oauth_signature),
                                       Uri.EscapeDataString(oauth_version)
            );


        ServicePointManager.Expect100Continue = false;
        resource_url += "?include_email=true";
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(resource_url);
        request.Headers.Add("Authorization", authHeader);
        request.Method = "GET";
        var response = request.GetResponse();
        return JsonConvert.DeserializeObject<TwitterDto>(new StreamReader(response.GetResponseStream()).ReadToEnd());
    }


public class TwitterDto
{
    public string name { get; set; }
    public string email { get; set; }
}

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