adds ability to set 'privateKey' file path

README.md

@@ -148,6 +148,28 @@ autossh({
 });
 ```
 
+#### Specifying the Private Key File
+
+Select a file from which the identity (private key) for public key authentication is read. The default is `~/.ssh/id_rsa`. 
+
+You can set the private file path as `privateKey` in the object you pass to `autossh`.
+
+```javascript
+autossh({
+  host: '111.22.333.444',
+  username: 'root',
+  localPort: 64444,
+  remotePort: 5432,
+  privateKey: '~/.ssh/github_rsa'
+})
+.on('error', err => {
+  console.error('ERROR: ', err);
+})
+.on('connect', connection => {
+  console.log('Tunnel established on port ' + connection.localPort);
+  console.log('pid: ' + connection.pid);
+});
+```
 
 #### Adjusting/Disabling Max Poll Count
 

index.js

@@ -49,6 +49,8 @@ var AutoSSH = function (_EventEmitter) {
 
     _this.serverAliveCountMax = typeof conf.serverAliveCountMax === 'number' ? conf.serverAliveCountMax : 1;
 
+    _this.privateKey = conf.privateKey || null;
+
     setImmediate(function () {
       var confErrors = _this.getConfErrors(conf);
 
@@ -180,14 +182,16 @@ var AutoSSH = function (_EventEmitter) {
     key: 'generateExecString',
     value: function generateExecString() {
       var bindAddress = this.localPort + ':localhost:' + this.remotePort;
-      var userAtHost = this.username + '@' + this.host;
       var exitOnFailure = '-o "ExitOnForwardFailure yes"';
       var serverAliveInterval = '-o ServerAliveInterval=' + this.serverAliveInterval;
       var serverAliveCountMax = '-o ServerAliveCountMax=' + this.serverAliveCountMax;
       var options = exitOnFailure + ' ' + serverAliveInterval + ' ' + serverAliveCountMax;
-      var execString = this.execString = 'ssh -NL ' + bindAddress + ' ' + options + ' ' + userAtHost;
+      var privateKey = this.privateKey ? '-i ' + this.privateKey : '';
+      var userAtHost = this.username + '@' + this.host;
 
-      return execString;
+      this.execString = 'ssh -NL ' + bindAddress + ' ' + options + ' ' + privateKey + ' ' + userAtHost;
+
+      return this.execString;
     }
 
     /*

src/index.js

@@ -25,6 +25,8 @@ class AutoSSH extends EventEmitter {
     this.serverAliveCountMax = typeof conf.serverAliveCountMax === 'number' ?
       conf.serverAliveCountMax : 1;
 
+    this.privateKey = conf.privateKey || null;
+
     setImmediate(() => {
       const confErrors = this.getConfErrors(conf);
 
@@ -148,14 +150,16 @@ class AutoSSH extends EventEmitter {
   */
   generateExecString() {
     const bindAddress = `${this.localPort}:localhost:${this.remotePort}`;
-    const userAtHost = `${this.username}@${this.host}`;
     const exitOnFailure = '-o "ExitOnForwardFailure yes"';
     const serverAliveInterval = `-o ServerAliveInterval=${this.serverAliveInterval}`;
     const serverAliveCountMax = `-o ServerAliveCountMax=${this.serverAliveCountMax}`;
     const options = `${exitOnFailure} ${serverAliveInterval} ${serverAliveCountMax}`;
-    const execString = this.execString = `ssh -NL ${bindAddress} ${options} ${userAtHost}`;
+    const privateKey = this.privateKey ? `-i ${this.privateKey}` : '';
+    const userAtHost = `${this.username}@${this.host}`;
 
-    return execString;
+    this.execString = `ssh -NL ${bindAddress} ${options} ${privateKey} ${userAtHost}`;
+
+    return this.execString;
   }
 
   /*