Implement TURN server authentication with hmac

This is a prefered method to allow limited access to the TURN server

Cargo.toml

@@ -79,6 +79,9 @@ num_cpus = "1.13.0"
 threadpool = "1.8.1"
 heed = { git = "https://github.com/timokoesters/heed.git", rev = "f6f825da7fb2c758867e05ad973ef800a6fe1d5d", optional = true }
 thread_local = "1.1.3"
+# used for TURN server authentication
+hmac = "0.11.0"
+sha-1 = "0.9.8"
 
 [features]
 default = ["conduit_bin", "backend_sqlite"]