public User Authenticate(string userName, string password)
        {
            var user = _user.SingleOrDefault(x => x.UserName == userName && x.Password == password);
            if (user==null)
            {
                return null;
            }
            //if user is not null then generate jwt token
            var tokenHandler = new JwtSecurityTokenHandler();
            var key = Encoding.ASCII.GetBytes(_appSettings);
            var tokenDescriptor = new SecurityTokenDescriptor
            {
                Subject = new ClaimsIdentity(new Claim[]
                {
                    new Claim(ClaimTypes.Name, user.Id.ToString())
                }),
                Expires = DateTime.Now.AddMinutes(5),
                SigningCredentials = new SigningCredentials(new SymmetricSecurityKey(key), SecurityAlgorithms.HmacSha256Signature)

            };
            var token = tokenHandler.CreateToken(tokenDescriptor);
            user.Token = tokenHandler.WriteToken(token);
            user.validFrom=token.ValidFrom;
            user.validTo = token.ValidTo;
            user.Password = null;
            return user;
        }
public static bool ValidateUser(string token, out string userid)
        {
            userid = null;
            var principle = GetPrincipal(token);
            if (principle==null)
            {
                return false;
            }
            var identity = principle.Identity as ClaimsIdentity;
            if (identity==null)
            {
                return false;
            }
            if (!identity.IsAuthenticated)
                return false;
            var useridClaim = identity.FindFirst(ClaimTypes.Name);
            userid = useridClaim.Value;
            if (string.IsNullOrEmpty(userid))
            {
                return false;
            }
            return true;

        }
    public static ClaimsPrincipal GetPrincipal(string token)
    {
        try
        {
            var tokenHandler = new JwtSecurityTokenHandler();
            var jwtToken = tokenHandler.ReadToken(token) as JwtSecurityToken;

            if (jwtToken == null)
                return null;

            var symmetricKey = Encoding.ASCII.GetBytes(AppSettings.Secret);

            var validationParameters = new TokenValidationParameters()
            {
                RequireExpirationTime = true,
                ValidateIssuer = false,
                ValidateAudience = false,
                IssuerSigningKey = new SymmetricSecurityKey(symmetricKey)
            };

            SecurityToken securityToken;
            var principal = tokenHandler.ValidateToken(token, validationParameters, out securityToken);

            return principal;
        }

        catch (Exception)
        {
            //should write log
            return null;
        }
    }