step towards customizable login functionality

customize.dist/credential.js

@@ -0,0 +1,77 @@
+define([
+    '/customize/application_config.js',
+    '/bower_components/scrypt-async/scrypt-async.min.js',
+], function (AppConfig) {
+    var Cred = {};
+    var Scrypt = window.scrypt;
+
+    Cred.MINIMUM_PASSWORD_LENGTH = typeof(AppConfig.minimumPasswordLength) === 'number'?
+        AppConfig.minimumPasswordLength: 8;
+
+    Cred.isLongEnoughPassword = function (passwd) {
+        return passwd.length >= Cred.MINIMUM_PASSWORD_LENGTH;
+    };
+
+    var isString = Cred.isString = function (x) {
+        return typeof(x) === 'string';
+    };
+
+    Cred.isValidUsername = function (name) {
+        return !!(name && isString(name));
+    };
+
+    Cred.isValidPassword = function (passwd) {
+        return !!(passwd && isString(passwd));
+    };
+
+    Cred.passwordsMatch = function (a, b) {
+        return isString(a) && isString(b) && a === b;
+    };
+
+    Cred.customSalt = function () {
+        return typeof(AppConfig.loginSalt) === 'string'?
+            AppConfig.loginSalt: '';
+    };
+
+    Cred.deriveFromPassphrase = function (username, password, len, cb) {
+        Scrypt(password,
+            username + Cred.customSalt(), // salt
+            8, // memoryCost (n)
+            1024, // block size parameter (r)
+            len || 128, // dkLen
+            200, // interruptStep
+            cb,
+            undefined); // format, could be 'base64'
+    };
+
+    Cred.dispenser = function (bytes) {
+        var entropy = {
+            used: 0,
+        };
+
+        // crypto hygeine
+        var consume = function (n) {
+            // explode if you run out of bytes
+            if (entropy.used + n > bytes.length) {
+                throw new Error('exceeded available entropy');
+            }
+            if (typeof(n) !== 'number') { throw new Error('expected a number'); }
+            if (n <= 0) {
+                throw new Error('expected to consume a positive number of bytes');
+            }
+
+            // grab an unused slice of the entropy
+            var A = bytes.slice(entropy.used, entropy.used + n);
+
+            // account for the bytes you used so you don't reuse bytes
+            entropy.used += n;
+
+            //console.info("%s bytes of entropy remaining", bytes.length - entropy.used);
+            return A;
+        };
+
+        return consume;
+    };
+
+    return Cred;
+});