update encryptLogin API

allow user to customize iterations and key length for encryptLogin method.
encryptLogin use pbkdf2 with a default 8192 iterations and 32 key length.

make pbkdf2 rounds a per-site password profile option
lesspass/lesspass#38

index.js

@@ -13,13 +13,11 @@ module.exports = {
     _createHmac
 };
 
-function _encryptLogin(login, masterPassword) {
+function _encryptLogin(login, masterPassword, {iterations = 8192, keylen = 32}={}) {
     return new Promise((resolve, reject) => {
         if (!login || !masterPassword) {
             reject('login and master password parameters could not be empty');
         }
-        const iterations = 8192;
-        const keylen = 32;
         crypto.pbkdf2(masterPassword, login, iterations, keylen, 'sha256', (error, key) => {
             if (error) {
                 reject('error in pbkdf2');

tests/api.tests.js

@@ -9,12 +9,37 @@ describe('LessPass', function () {
             });
         });
 
+        it('should allow to customize number of iterations', function (done) {
+            LessPass.encryptLogin('test@example.org', 'password', {iterations: 4096}).then(function (encryptedLogin) {
+                assert.equal('0a91208545e3aa4935d3a22984ca097a7669259a04d261ac16361bdc1a2e960f', encryptedLogin);
+                done();
+            });
+        });
+
+        it('should allow to customize key length', function (done) {
+            LessPass.encryptLogin('test@example.org', 'password', {keylen: 16}).then(function (encryptedLogin) {
+                assert.equal('d8af5f918db6b65b1db3d3984e5a400e', encryptedLogin);
+                done();
+            });
+        });
+
+        it('should allow to customize iterations and key length', function (done) {
+            LessPass.encryptLogin('test@example.org', 'password', {
+                iterations: 4096,
+                keylen: 16
+            }).then(function (encryptedLogin) {
+                assert.equal('0a91208545e3aa4935d3a22984ca097a', encryptedLogin);
+                done();
+            });
+        });
+
         it('should allow utf8 parameter', function (done) {
             LessPass.encryptLogin('test@example.org', '♥ LessPass ♥').then(function (encryptedLogin) {
                 assert.equal('997fe81d3d0db236e039c75efdb487f17a902fdf94f9dacaa9884329c85d9651', encryptedLogin);
                 done();
             });
         });
+
         it('auto generated encrypt login tests', function () {
             var promises = [];
             var passwords = [
@@ -105,6 +130,8 @@ describe('LessPass', function () {
                 assert.equal('azYS7,olOL2]', generatedPassword);
             })
         });
+
+
         it('auto generated render password tests', function () {
             var promises = [];
             var passwords = [