title: App crashing when using Firebase Auth, reason: 'Default app has already been configured.'
body: <p>I'm building my first iOS application, and I am using Firebase to handle authentication, database, etc. I added a sign up screen and used the following code to create a new user: </p>
  
  <pre><code>FIRAuth.auth()?.createUserWithEmail(emailAddress.text!, password: password.text!, completion: { (user, error) in
  
          })
  </code></pre>
  
  <p>When the user taps on the sign up button, there is a segue that should take them back to the original login view controller. However, when I got to run the app, it hangs on the launch screen. Here is the debugger output:</p>
  
  <pre><code>2016-06-19 14:35:05.402 unitaskr[4386:82981] Configuring the default app.
  2016-06-19 14:35:05.413 unitaskr[4386:] &lt;FIRAnalytics/INFO&gt; Firebase Analytics     v.3200000 started
  2016-06-19 14:35:05.414 unitaskr[4386:] &lt;FIRAnalytics/INFO&gt; To enable debug logging set the following application argument: -FIRAnalyticsDebugEnabled (see ...)
  2016-06-19 14:35:05.419: &lt;FIRInstanceID/WARNING&gt; FIRInstanceID AppDelegate proxy enabled, will swizzle app delegate remote notification handlers. To disable add "FirebaseAppDelegateProxyEnabled" to your Info.plist and set it to NO
  2016-06-19 14:35:05.418 unitaskr[4386:] &lt;FIRAnalytics/INFO&gt; Successfully created Firebase Analytics App Delegate Proxy automatically. To disable the proxy, set the flag FirebaseAppDelegateProxyEnabled to NO in the Info.plist
  2016-06-19 14:35:05.430 unitaskr[4386:82981] *** Terminating app due to uncaught exception 'com.firebase.core', reason: 'Default app has already been configured.'
  *** First throw call stack:
  (
  0   CoreFoundation                      0x00000001100a8d85   __exceptionPreprocess + 165
  1   libobjc.A.dylib                     0x00000001108e7deb objc_exception_throw + 48
  2   CoreFoundation                      0x00000001100a8cbd +[NSException raise:format:] + 205
  3   unitaskr                            0x000000010b58844d +[FIRApp    configureDefaultAppWithOptions:sendingNotifications:] + 102
  4   unitaskr                            0x000000010b588238 +[FIRApp configure] + 302
  5   unitaskr                            0x000000010b541f1a _TFC8unitaskr11AppDelegate11applicationfTCSo13UIApplication29didFinishLaunchingWithOptionsGSqGVs10DictionaryCSo8NSObjectPs9AnyObject____Sb + 266
  6   unitaskr                            0x000000010b542204 _TToFC8unitaskr11AppDelegate11applicationfTCSo13UIApplication29didFinishLaunchingWithOptionsGSqGVs10DictionaryCSo8NSObjectPs9AnyObject____Sb + 180
  7   UIKit                               0x000000010e5bf9ac -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 272
  8   UIKit                               0x000000010e5c0c0d -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 3415
  9   UIKit                               0x000000010e5c7568 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1769
  10  UIKit                               0x000000010e5c4714 -[UIApplication workspaceDidEndTransaction:] + 188
  11  FrontBoardServices                  0x00000001127b78c8 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 24
  12  FrontBoardServices                  0x00000001127b7741 -[FBSSerialQueue _performNext] + 178
  13  FrontBoardServices                  0x00000001127b7aca -[FBSSerialQueue _performNextFromRunLoopSource] + 45
  14  CoreFoundation                      0x000000010ffce301 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
  15  CoreFoundation                      0x000000010ffc422c __CFRunLoopDoSources0 + 556
  16  CoreFoundation                      0x000000010ffc36e3 __CFRunLoopRun + 867
  17  CoreFoundation                      0x000000010ffc30f8 CFRunLoopRunSpecific + 488
  18  UIKit                               0x000000010e5c3f21 -[UIApplication _run] + 402
  19  UIKit                               0x000000010e5c8f09 UIApplicationMain + 171
  20  unitaskr                            0x000000010b542a42 main + 114
  21  libdyld.dylib                       0x00000001113b692d start + 1
  )
  libc++abi.dylib: terminating with uncaught exception of type NSException
  (lldb) 
  </code></pre>
  
  <p>I can provide additional information as needed, any help/advice would be greatly appreciated as I am just starting out and looking to learn as much as possible. Have a great day! </p>