Mime::base64::urlsafe is a perl version of python's url-safe base64 encoder / decoder.

when embedding binary data in url, it is preferable to use base64 encoding. however, two characters ('+' and '/') used in the standard base64 encoding have special meanings in urls, often leading to re-encoding with url-encoding, or worse, interoperability problems.

to overcome the problem, the module provides a variation of base64 codec compatible with python's urlsafe_b64encode / urlsafe_b64decode