PAM module to authenticate users running a SLURM job and track their processes

 Pluggable Authentication Module (PAM) for restricting access to compute
 nodes where SLURM performs resource management to users who have a
 running job. The user's connection is "adopted" into the "external"
 step of the job so that processes spawned are tracked and SLURM can
 perform a complete cleanup when the job is completed.