Installing the pegasus python modules fails as it requires an old (buggy) version of pyOpenSSL:

pip install http://download.pegasus.isi.edu/pegasus/4.8.0/pegasus-python-source-4.8.0.tar.gz

gcc -pthread -fno-strict-aliasing -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv -DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv -fPIC -I/usr/include/python2.7 -c OpenSSL/crypto/crl.c -o build/temp.linux-x86_64-2.7/OpenSSL/crypto/crl.o
OpenSSL/crypto/crl.c:6:23: error: static declaration of ‘X509_REVOKED_dup’ follows non-static declaration
static X509_REVOKED * X509_REVOKED_dup(X509_REVOKED *orig) {
^
In file included from /usr/include/openssl/ssl.h:156:0,
from OpenSSL/crypto/x509.h:17,
from OpenSSL/crypto/crypto.h:30,
from OpenSSL/crypto/crl.c:3:
/usr/include/openssl/x509.h:751:15: note: previous declaration of ‘X509_REVOKED_dup’ was here
X509_REVOKED *X509_REVOKED_dup(X509_REVOKED *rev);
^
error: command 'gcc' failed with exit status 1

The solution is to require pyOpenSSL-17.3.0 in the setup.py file.