cli: add stdio control server

* signing: implement signing service on the web

* wip

* cli: implement stdio service

This is used to implement the exec server for WSL. Guarded behind a signed handshake.

* update distro

* rm debug

* address pr comments

cli/src/tunnels/challenge.rs

@@ -0,0 +1,41 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+#[cfg(not(feature = "vsda"))]
+pub fn create_challenge() -> String {
+	use rand::distributions::{Alphanumeric, DistString};
+	Alphanumeric.sample_string(&mut rand::thread_rng(), 16)
+}
+
+#[cfg(not(feature = "vsda"))]
+pub fn sign_challenge(challenge: &str) -> String {
+	use sha2::{Digest, Sha256};
+	let mut hash = Sha256::new();
+	hash.update(challenge.as_bytes());
+	let result = hash.finalize();
+	base64::encode_config(result, base64::URL_SAFE_NO_PAD)
+}
+
+#[cfg(not(feature = "vsda"))]
+pub fn verify_challenge(challenge: &str, response: &str) -> bool {
+	sign_challenge(challenge) == response
+}
+
+#[cfg(feature = "vsda")]
+pub fn create_challenge() -> String {
+	use rand::distributions::{Alphanumeric, DistString};
+	let str = Alphanumeric.sample_string(&mut rand::thread_rng(), 16);
+	vsda::create_new_message(&str)
+}
+
+#[cfg(feature = "vsda")]
+pub fn sign_challenge(challenge: &str) -> String {
+	vsda::sign(challenge)
+}
+
+#[cfg(feature = "vsda")]
+pub fn verify_challenge(challenge: &str, response: &str) -> bool {
+	vsda::validate(challenge, response)
+}