SAML payload larger than expected (mod_auth_cas and proxy_fcgi)

[Alan S]

I don't believe this is an issue with mod_auth_cas, but I could use some direction.

A user with a large SAML memberships payload is not passing authentication due to the length:

[proxy_fcgi:warn] [pid 750194] [client xxx.xxx.xxx.xxx:57500] AH02536: couldn't encode envvar 'HTTP_SAML_MEMBEROF' in 16384 bytes

The total memberof attributes size is ~30 bytes, but I'm not sure where to increase this limit in the FCGI proxy module, or if, indeed, this is a good idea. For reference:

https://sources.debian.org/src/apache2/2.4.10-10+deb8u12/modules/proxy/mod_proxy_fcgi.c/#L237

Has anyone else experienced this that could provide some pointers?

Thank you!

-Alan