Changing the scheme of System.Uri

Another iteration on Good Night Nerd Pride's answer, as an extension:

public static Uri RewriteHttps(this Uri originalUri)
{
    return new UriBuilder(originalUri)
    {
        Scheme = Uri.UriSchemeHttps,
        Port = originalUri.IsDefaultPort ? -1 : originalUri.Port // -1 => default port for scheme
    }.Uri;
}

I prefer to pass the desired https port number into the ForceHttps method if you want to use a custom one otherwise omit the https port or use -1 to use the standard one (implicitly). I don't really bother with the port that is already on the url because http and https can never use the same port on the same server.

In the event that the url is already https, it will pass through unchanged leaving whatever port is there in place.

private static string ForceHttps(string requestUrl, int? httpsPort = null)
{
    var uri = new UriBuilder(requestUrl);
    // Handle https: let the httpsPort value override existing port if specified
    if (uri.Uri.Scheme.Equals(Uri.UriSchemeHttps)) {
        if (httpsPort.HasValue)
            uri.Port = httpsPort.Value;
        return uri.Uri.AbsoluteUri;
    }

    // Handle http: override the scheme and use either the specified https port or the default https port
    uri.Scheme = Uri.UriSchemeHttps;
    uri.Port = httpsPort.HasValue ? httpsPort.Value : -1;

    return uri.Uri.AbsoluteUri;
}

Usage:

ForceHttps("http://www.google.com/"); // https://www.google.com/
ForceHttps("http://www.google.com/", 225); // https://www.google.com:225/
ForceHttps("http://www.google.com/", 443); // https://www.google.com:443/
ForceHttps("https://www.google.com/"); // https://www.google.com/
ForceHttps("https://www.google.com:443/"); // https://www.google.com:443/
ForceHttps("https://www.google.com:443/", -1); // https://www.google.com/
ForceHttps("http://www.google.com:80/"); // https://www.google.com/
ForceHttps("http://www.google.com:3000/", 8080); // https://www.google.com:8080/

Ended up with this one:

var uriBuilder = new UriBuilder(requestUrl)
{
    Scheme = Uri.UriSchemeHttps,
    Port = -1 // default port for scheme
};

var uri = uriBuilder.Uri;

UserControl's answer works fine unless you have to make sure non-default ports are preserved in the URI.

For instance, http://localhost:12345/hello should become https://localhost:12345/hello instead of https://localhost/hello.

Here's how to do that easily:

public static string ForceHttps(string requestUrl)
{
    var uri = new UriBuilder(requestUrl);

    var hadDefaultPort = uri.Uri.IsDefaultPort;
    uri.Scheme = Uri.UriSchemeHttps;
    uri.Port = hadDefaultPort ? -1 : uri.Port;

    return uri.ToString();
}

Note that we have to read uri.Uri.IsDefaultPort before setting uri.Scheme.

Here is a working example: https://dotnetfiddle.net/pDrF7s