using System;

public class Program

{

​

    public static void Main()

    {                           

        string userInput = "https://git.example.com/test/";

​

        if (isSafeURL(userInput))

        {

            Console.WriteLine("safe");

        }

        else

        {

            Console.WriteLine("unsafe");

        }

    }

    static string[] validBaseURLs = new string[] { 

            "https://wiki.example.com/",

            "https://jira.example.com/",

            "https://git.example.com/",

        };

    public static bool isSafeURL(string untrustedURL)

    {

        foreach (string baseURL in validBaseURLs)

        {

            if (validateBaseURL(untrustedURL, baseURL))

                return true;

        }

        return false;

    }

    // based on example from https://docs.microsoft.com/en-us/dotnet/api/system.uri?view=net-5.0

    public static bool validateBaseURL(string untrustedURL, string baseURL)

    {

        Uri baseUri = new Uri(baseURL);

​

        if (!Uri.TryCreate(baseUri, untrustedURL, out Uri newUri))

        {

            // Fail: invalid input.

            return false;

        }

​

        if (!baseUri.IsBaseOf(newUri))

        {

            // Fail: the Uri base has been modified - the created Uri is not rooted in the original directory.

            return false;

        }   

        return true;

    }

}