https://github.com/digitalbazaar/forge#pki

Javascript implementation of PKI, I don't know if they have v15 though.

That's a good comment.

golang has a library that implements the ssh-agent protocol, while forge doesn't, which makes it hard to use forge for macgyver's use case.

It's possible to use golang's ssh library with a non-golang RSA implementation. Which could be forge, web crypto, or other. I am likely to do this.

I mainly submitted this issue in case gopherjs is interested in improving the situation (or even just documenting why it's slow for anyone googling to find out why).

I think this could be a good test case for GopherJS performance improvements (as well as the slow-running tests in the crypto/x509 package). A while ago I attempted to profile these and determined that it was due to GopherJS's inefficient array access operations. One particular suspect is the range check GopherJS inserts on every array/slice element access.