Thanks to [email protected], who has finished my PR, the Nhrp Cisco auth was merged today.
https://github.com/FRRouting/frr/pull/16172

Looking at it, T5816 already attempted to fix this and is probably better for users - doesn't give the full flexibility of regex and doesn't handle '_' at all, but does have a strict format expectation.

Looking at the code in FRR, it just expands '_' to the full match '(^|[,{}()]|$)' and sends that whole match off to regexec().

All working nicely in current rolling.

@Thunderstorm looks like this one made it to the current rolling, if you're able to try it out?

https://github.com/vyos/vyos-1x/pull/3677

https://github.com/part1cleth1ef/vyos-1x

https://github.com/vyos/vyos-1x/pull/3652

all work!
Thank you

@pavel-altair can you please re-test with VyOS 1.5-rolling-202406170021