Allow key to be specified or generated for crypto_auth

Author: Face Kapow

js/core/libsodium.js

@@ -26,7 +26,7 @@ function hexToU8(hexStr) {
   return u8;
 }
 
-function stringOrU8(arg, funcName, argName, i) {
+function stringOrU8(arg, funcName, argName, i, msg) {
   var ret = arg;
   if (!(arg instanceof Uint8Array)) {
     if (typeof arg === 'string') {
@@ -35,7 +35,7 @@ function stringOrU8(arg, funcName, argName, i) {
         ret[i] = arg.charCodeAt(i);
       }
     } else {
-      throw new Error(funcName + ': ' + argName + '(argument ' + i + ') must be a string or Uint8Array.');
+      throw new Error(funcName + ': ' + argName + '(argument ' + i + ') ' + (msg ? msg : 'must be a string or Uint8Array') + '.');
     }
   }
   return ret;
@@ -68,18 +68,22 @@ module.exports = {
     }
     return hexToU8(decipher);
   },
-  crypto_auth: function(data) {
+  crypto_auth: function(data, key) {
     var dataArr = stringOrU8(data, 'crypto_auth', 'data', 0);
+    var keyArr;
+    if (key === null || key === undefined) {
+      keyArr = runtime.random.getRandomValues(constants.crypto_auth_KEYBYTES);
+    } else {
+      keyArr = stringOrU8(key, 'crypto_auth', 'key', 1, 'must be unspecified, a string, or Uint8Array');
+    }
 
-    var key = runtime.random.getRandomValues(constants.crypto_auth_KEYBYTES);
-
-    var mac = lib.crypto_auth(dataArr, key);
+    var mac = lib.crypto_auth(dataArr, keyArr);
     if (!mac) {
       throw new Error('crypto_auth: error creating tag.');
     }
     return {
       mac: hexToU8(mac),
-      key: key
+      key: keyArr
     };
   },
   crypto_auth_verify: function(mac, key, data) {