This document defines a mechanism (flags and sub-TLV) to advertise via the PCE
Protocol security required within the IGP being used.

This is a very well written, clear, and sensible document. In my opinion, it is 
Ready.

Flagging some potential nits:

Abstract:
Old:
   capability.  Further, this document updates RFC 8231, and RFC 8306.
New:
   capability.  Further, this document updates RFC 8231 and RFC 8306.

Question:
The header and Section 4 say this updates RFCs 5088 and 5089; however, 
that is not mentioned in the Abstract.

Old:
   The YANG model for PCEP [I-D.ietf-pce-pcep-yang] supports PCEP
   security parameters (key, key chain and TLS).
New:
   The YANG model for PCEP [I-D.ietf-pce-pcep-yang] supports PCEP
   security parameters (key, key chain, and TLS).

Thanks!

Carlos.