Added ability to programmatically submit a MFA code to Robinhood

When calling User.authenticate(), a function can be passed to automatically retrieve the multi-factor authentication code from Robinhood

README.md

@@ -109,12 +109,28 @@ Personally, I either store user data as an array in a .json file, then require i
 
 ##### MFA
 
-Algotrader now supports multifactor authentication. So, if you have this enabled on your account (which is a good idea by the way), you'll be prompted to enter the six-digit code after login. If you run a trading script with this library automatically and have MFA enabled, it may be worth your while to utilize a telecom API (possible through Twilio?) to have the code programmatically entered into the CLI.
+Algotrader now supports multi-factor authentication. So, if you have this enabled on your account (which is a good idea by the way), you'll be prompted to enter the six-digit code after login. If you run a trading script with this library automatically and have MFA enabled, it may be worth your while to utilize a telecom API (possible through Twilio?) to have the code programmatically entered into the CLI (see below).
 
 The MFA prompt will appear like so:
 
 ![Algotrader MFA Prompt](https://i.gyazo.com/11420983d69bf02a59026947513408ac.png)
 
+To enter the code programmatically, you can pass a function to [```User.authenticate()```](https://github.com/Ladinn/algotrader/blob/master/docs/ROBINHOOD.md#User) that returns a promise containing the MFA code in a six-character string. For example:
+
+```js
+function getMFA() {
+	return new Promise((resolve, reject) => {
+    	// Get the code here
+        const mfa = "123456"
+        resolve(mfa);
+    })
+}
+myUser.authenticate(getMFA)
+	.then(() => {
+		// User was authenticated
+	})
+```
+
 #### Get a user's portfolio
 There are a good amount of query functions that you can run on the user's portfolio. Using your [```User```](https://github.com/Ladinn/algotrader/blob/master/docs/ROBINHOOD.md#User) instance, you can grab the portfolio using ``` User.getPortfolio()``` which returns a new [```Portfolio```](https://github.com/Ladinn/algotrader/blob/master/docs/ROBINHOOD.md#Portfolio) object.
 ```js

docs/ROBINHOOD.md

@@ -1150,7 +1150,7 @@ Represents the user that is logged in while accessing the Robinhood API.
 
 * [User](#User)
     * [new User(username, password)](#new_User_new)
-    * [.authenticate()](#User+authenticate) ⇒ <code>Promise.&lt;Boolean&gt;</code>
+    * [.authenticate(mfaFunction)](#User+authenticate) ⇒ <code>Promise.&lt;Boolean&gt;</code>
     * [.logout()](#User+logout) ⇒ <code>Promise.&lt;Boolean&gt;</code>
     * [.getAccount()](#User+getAccount) ⇒ <code>Promise</code>
     * [.getBalances()](#User+getBalances) ⇒ <code>Promise.&lt;Object&gt;</code>
@@ -1185,10 +1185,15 @@ Creates a new User object.
 
 <a name="User+authenticate"></a>
 
-### user.authenticate() ⇒ <code>Promise.&lt;Boolean&gt;</code>
+### user.authenticate(mfaFunction) ⇒ <code>Promise.&lt;Boolean&gt;</code>
 Authenticates a user using the inputted username and password.
 
 **Kind**: instance method of [<code>User</code>](#User)  
+
+| Param | Type | Description |
+| --- | --- | --- |
+| mfaFunction | <code>function</code> \| <code>Null</code> | Optional function that is called when prompted for multi-factor authentication. Must return a promise with a six-character string. If not provided the CLI will be prompted. |
+
 <a name="User+logout"></a>
 
 ### user.logout() ⇒ <code>Promise.&lt;Boolean&gt;</code>

objects/broker/robinhood/User.js

@@ -31,9 +31,10 @@ class User extends Robinhood {
 
 	/**
 	 * Authenticates a user using the inputted username and password.
+	 * @param {Function|Null} mfaFunction - Optional function that is called when prompted for multi-factor authentication. Must return a promise with a six-character string. If not provided the CLI will be prompted.
 	 * @returns {Promise<Boolean>}
 	 */
-	authenticate() {
+	authenticate(mfaFunction) {
 		const _this = this;
 		return new Promise((resolve, reject) => {
 			if (_this.password == null) {
@@ -67,36 +68,54 @@ class User extends Robinhood {
 				else {
 					const json = JSON.parse(body);
 					if (json.mfa_required) {
-						console.log("Multifactor authentication detected. Please enter your six-digit code below:");
-						prompt.get({
-							properties: {
-								code: {
-									pattern: /^[0-9]{6}$/,
-									message: "Your Robinhood code will most likely be texted to you and should only contain 6 integers.",
-									required: true
+						if (mfaFunction !== undefined) {
+							console.log("Multi-factor authentication detected. Executing the provided function...");
+							mfaFunction()
+								.then(mfa => {
+									if (!mfa instanceof String) reject(new Error("The provided function did not return a string after the promise resolved."));
+									else if (mfa.length !== 6) reject(new Error("The provided function returned a string, but it is not six-characters in length."));
+									else _sendMFA(mfa, resolve, reject);
+								})
+								.catch(error => {
+									console.log("An error occurred while executing the provided MFA function.");
+									reject(error);
+								})
+						} else {
+							console.log("Multi-factor authentication detected. Please enter your six-digit code below:");
+							console.log(" - This can be entered programmatically by passing a function when authenticating. See documentation for more.");
+							prompt.get({
+								properties: {
+									code: {
+										pattern: /^[0-9]{6}$/,
+										message: "Your Robinhood code will most likely be texted to you and should only contain 6 integers.",
+										required: true
+									}
 								}
-							}
-						}, (error, result) => {
-							request.post({
-								uri: _this.url + '/oauth2/token/',
-								form: {
-									username: _this.username,
-									password: _this.password,
-									client_id: 'c82SH0WZOsabOXGP2sxqcj34FxkvfnWRZBKlBjFS',
-									grant_type: 'password',
-									scope: 'internal',
-									mfa_code: result.code
-								}
-							}, (error, response, body) => {
-								if (error) reject(error);
-								else if (response.statusCode !== 200) reject(new LibraryError(body));
-								else _postAuth(JSON.parse(body), resolve, reject);
+							}, (error, mfaCode) => {
+								_sendMFA(mfaCode.code, resolve, reject);
 							})
-						})
+						}
 					} else _postAuth(json, resolve, reject);
 				}
 			})
 		}
+		function _sendMFA(mfaCode, resolve, reject) {
+			request.post({
+				uri: _this.url + '/oauth2/token/',
+				form: {
+					username: _this.username,
+					password: _this.password,
+					client_id: 'c82SH0WZOsabOXGP2sxqcj34FxkvfnWRZBKlBjFS',
+					grant_type: 'password',
+					scope: 'internal',
+					mfa_code: mfaCode
+				}
+			}, (error, response, body) => {
+				if (error) reject(error);
+				else if (response.statusCode !== 200) reject(new LibraryError(body));
+				else _postAuth(JSON.parse(body), resolve, reject);
+			})
+		}
 		function _postAuth(json, resolve, reject) {
 			_this.token = json.access_token;
 			_this.getAccount().then(account => {

package.json

@@ -1,6 +1,6 @@
 {
   "name": "algotrader",
-  "version": "1.4.1",
+  "version": "1.4.2",
   "description": "Algorithmically trade stocks and options using Robinhood, Yahoo Finance, and more.",
   "main": "index.js",
   "scripts": {