Read passphrase from AGE_PASSPHRASE env var if available

[KasteloShep]

From jjlin's own forked commit of age that allows env var to supply the passphrase for automated encryption processes

https: //github.com/jjlin/age/commit/2afaf7fda78117f1e0b784a8c41f9dea15028316
Co-Authored-By: Jeremy Lin 203380+jjlin@users.noreply.github.com

[jjlin]

I didn't send a PR for this because @FiloSottile seems undecided on whether he wants to add this capability. And if it were really to be implemented, there are a few other places that should read from env var, like the decryption paths.

[tbugfinder]

Especially in a pipeline environment this makes sense to me.

[FiloSottile]

I've decided we won't provide alternative password input methods in cmd/age, but we'll ship them all in a separate plugin, like sshpass. I'll make sure to support an environment variable there, and I'll update discussion #256 when it's ready. See #256 (comment) for a bit more details. Thank you!

[mirql]

also ill put it here, in case anyone searching also

using "expect"

#520 (comment)

[FiloSottile]

The new batchpass plugin handles non-interactive passphrase encryption. See #256 (comment) for usage and a warning.