We added a new custom authentication provider (saml2) and needed to customize our logout url based on what someone logged in with.

Credit to Velizar Bishurov for the answer

GetIdp.csView on GitHub
    public static class Util
    {
        public static string GetIdentityProvider()
        {
            var identity = ClaimsManager.GetCurrentIdentity();
            var idToken = identity.Claims.FirstOrDefault(c => c.Type == "id_token");
            if (idToken != null)
            {
                var handler = new JwtSecurityTokenHandler();
                var jwtToken = handler.ReadToken(idToken.Value) as JwtSecurityToken;
                if (jwtToken != null)
                {
                    var idpClaim = jwtToken.Claims.FirstOrDefault(c => c.Type == "idp");
                    if (idpClaim != null)
                    {
                        return idpClaim.Value;
                    }
                }
            }

            return "Unknown";
        }
  }