Python 3.13 Compatibility

[ephes]

Hi there,

First off, thank you for this amazing library! I recently wrote a blog post demonstrating how to use Django as a service provider, with pysaml2 serving as an example IdP. A reader has since pointed out that it doesn’t work with Python 3.13, and after some investigation, I suspect the issue stems from the removal of the cgi module in Python 3.13.

I noticed that pysaml2 still imports cgi in a couple of places. For example:

In src/saml2/httputil.py:

# The `cgi` module is used here:
formdata = cgi.parse(environ["wsgi.input"], environ, empty, err)

# Since `parse_qs` is already imported, this could potentially be replaced with:
input_stream = environ["wsgi.input"]
content_length = int(environ.get("CONTENT_LENGTH", 0))
form_data_bytes = input_stream.read(content_length)
form_data = parse_qs(form_data_bytes.decode('utf-8'))

In src/saml2/pack.py and src/saml2/httputil.py:

# The fallback to `cgi` for HTML escaping could be removed, as the `html` module 
# (introduced in Python 3.4) provides the necessary functionality:
try:
    import html
except Exception:
    import cgi as html  # type: ignore[no-redef]

Would it make sense to update these references to make pysaml2 compatible with Python 3.13? I’d be happy to help test any changes.

Best regards, Jochen

[c00kiemon5ter]

Would you like to make a PR with this change? I'd be happy to accept it.