Passing arguments with special characters I want to pass a token into my custom module via the URL, like so:

http://example.com/myurl?token=ffjei4T93F/ggF0PImZxlDWSR8JYHaPmkkjLSUVSKkr

Drupal has issues with passing tokens using clean URLs:

https://www.drupal.org/node/118072

...and because my token has a '/' forward slash in it it breaks if I use arg(1) to get the token.

What to do?
For Drupal 7, use drupal_get_query_parameters().

https://api.drupal.org/api/drupal/includes%21common.inc/function/drupal_get_query_parameters/7.x