NHRP authentication not compliant with RFC 2332

[zmw12306]

The current NHRP implementation uses a Cisco-style static secret in the NHRP_EXTENSION_AUTHENTICATION extension. However, RFC 2332 (Section 5.3.4.3) specifies that authentication should use SPI-based lookup and hash calculation, not direct secret comparison.

This Cisco-style format doesn't include SPI or hashing and doesn't follow the RFC-defined structure. According to the RFC, vendor-specific formats like this should be placed in a Vendor-Private Extension (Type 8), not in the standard authentication type.

Is this behavior intentional for Cisco compatibility? If so, would it make sense to either:

move it into a vendor-private extension, or
clarify in the docs that this is not RFC-compliant?