I found an EPEL mirror that keeps previous versions of packages: https://mirror.umd.edu/fedora/epel/
You can either make this your default mirror for the EPEL repo, or you can manually download the previous versions of the packages from there and then run the yum downgrade. I downgraded to 2.16.1 and things are working for me in RHEL7.
Note that WeBWorK doesn't require libapreq2-devel to be installed. You would only need this if you needed to compile something from source that depended on libapreq. With that being said, if you have it installed it will need to be downgraded at the same time as the other packages as Justin mentioned.
@Justin, Casey, Danny:
Thank you all for this.
For those who also have the same issue and struggling to find the steps, here's what I did following the above suggestions / information:
0/ You can verify, if you want, what's installed with
sudo yum --showduplicates list *libapreq2
1/ Download the 2.16-1-1.el7 package from https://koji.fedoraproject.org/koji/buildinfo?buildID=1747448
(I have 2 relevant packages libapreq2.x86_64 and perl-libapreq2.x86_64 so I downloaded those two)
2/ Downgrade using the two packages you just downloaded
sudo rpm -Uvh --oldpackage libapreq2-2.16-1.el7.x86_64.rpm
sudo rpm -Uvh --oldpackage perl-libapreq2-2.16-1.el7.x86_64.rpm
Can verify with the same command sudo yum --showduplicates list *libapreq2
Hope that helps someone.
It's worth noting that version 2.18 of WeBWorK no longer uses Apache/mod_perl, and thus no longer needs Apache::Request.
Since 2.18 is built on Mojolicious it will be much easier to run on current linux distributions.