Normalize email input for registration and login

Trim and lowercase email before storing or attempting login to avoid mismatches from case or surrounding whitespace. Updated RegisteredUserController@store to save 'email' => strtolower(trim($request->email)) and LoginRequest@authenticate to call Auth::attempt with the normalized email input.

app/Http/Requests/Auth/LoginRequest.php

@@ -45,7 +45,7 @@ class LoginRequest extends FormRequest
     {
         $this->ensureIsNotRateLimited();
 
-        if (! Auth::attempt($this->only('email', 'password'), $this->boolean('remember'))) {
+        if (! Auth::attempt(['email' => strtolower(trim($this->input('email'))), 'password' => $this->input('password')], $this->boolean('remember'))) {
             RateLimiter::hit($this->throttleKey());
 
             throw ValidationException::withMessages([