[cli] Add --code and --delete options to auth command

--code allows specifying an exchange code directly, e.g.
       when the web authentication is handled by an external
       application.
--delete simply deletes the current authentication data.

legendary/cli.py

@@ -43,12 +43,15 @@ class LegendaryCLI:
         return ql
 
     def auth(self, args):
+        if args.auth_delete:
+            self.core.lgd.invalidate_userdata()
+            return
+
         try:
             logger.info('Testing existing login data if present...')
             if self.core.login():
                 logger.info('Stored credentials are still valid, if you wish to switch to a different '
-                            'account, delete ~/.config/legendary/user.json and try again.')
-                exit(0)
+                            'account, run "legendary auth --delete" and try again.')
         except ValueError:
             pass
         except InvalidCredentialsError:
@@ -69,6 +72,7 @@ class LegendaryCLI:
                 logger.error('No EGS login session found, please login normally.')
                 exit(1)
 
+        if not args.auth_code:
             # unfortunately the captcha stuff makes a complete CLI login flow kinda impossible right now...
             print('Please login via the epic web login!')
             webbrowser.open(
@@ -80,6 +84,8 @@ class LegendaryCLI:
                   'in your web browser after you have finished logging in.')
             exchange_code = input('Please enter code from JSON response: ')
             exchange_token = exchange_code.strip().strip('"')
+        else:
+            exchange_token = args.auth_code
 
         if self.core.auth_code(exchange_token):
             logger.info(f'Successfully logged in as "{self.core.lgd.userdata["displayName"]}"')
@@ -479,6 +485,10 @@ def main():
     if os.name == 'nt':
         auth_parser.add_argument('--import', dest='import_egs_auth', action='store_true',
                                  help='Import EGS authentication data')
+    auth_parser.add_argument('--code', dest='auth_code', action='store', metavar='<exchange code>',
+                             help='Use specified exchange code instead of interactive authentication.')
+    auth_parser.add_argument('--delete', dest='auth_delete', action='store_true',
+                             help='Remove existing authentication data')
 
     install_parser.add_argument('--base-path', dest='base_path', action='store', metavar='<path>',
                                 help='Path for game installations (defaults to ~/legendary)')