RFE: Allow use of ssh public key *path* rather than key contents for recipient

[larsks]

Environment

• OS: fedora 30
• age version: e43cf8b

What were you trying to do

I wish that I could encrypt to a public key by specifying a path to the public key file:

age -r ~/keys/someperson.pub

Rather than the *contents * of the public key file:

age -r $(cat ~/keys/someperson.pub)

(Maybe this would require a new option (-R?) rather than overloading the behavior of the existing --recipient/-r option)

And obviously it would be nice if this same feature were available for age public keys as well.

[cyb3rz3us]

If possible, I would vote for using the same '-r' but if not feasible, then whatever works to get this implemented.

[nxg]

(This comment may be redundant, given the presence of the linked pull request; if so, just ignore)

Another possibility is to distinguish a key-file from a key by prefixing it with @

age -r @~/keys/someperson.pub

(curl --data-binary has a syntax like this, if it's useful to quote a precedent).

Another possibility is to regard the -r option value as referring to a file if there's a file by that name, and as an explicit key otherwise. It's true that adds a heuristic element, but it's only likely to get the wrong answer if there is (deliberately, mischievously, or accidentally) a file which shares its name with a key-value.

Adding file:// URLs is cute, and very general, but not massively easier to script (which is the real problem with the key-only value for -r). Excess generality can be a vice, as well, especially if it requires that other libraries be pulled in.

Overall, adding -R seems simpler.