doc,test: clarify ChaCha20-Poly1305 usage
The crypto documentation does not list chacha20-poly1305
as a supported AEAD algorithm and omits that the algorithm requires passing the authTagLength
option.
This patch changes that and also adds a test to assert that the documented behavior is correct.
Arguably, chacha20-poly1305
should not require the authTagLength
option. I'll probably open a separate semver-minor PR to address that and update the documentation accordingly.