Build refresh token method from token handler of JWT API.

TokenHandler.cs

private RefreshToken BuildRefreshToken(User user)
{
    var refreshToken = new RefreshToken
    (
        token : _passwordHaser.HashPassword(Guid.NewGuid().ToString()),
        expiration : DateTime.UtcNow.AddSeconds(_tokenOptions.RefreshTokenExpiration).Ticks
    );

    return refreshToken;
}