.env file, and configuration variables with newlines

Moving this on behalf of @JeanMertz from https://github.com/deis/controller/issues/891

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I've seen this issue being tested in #268, except that that involves deis config:set, not deis config:push.

I have a .env file, that I want to contain a public key:

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEMF802GSVwt2ZsFlmYR6Yy4rzZR8A
o5XaElze2V5JBjeT4fUnGrK0mjvYK/CTaCVHTwq8QsC1osfN7OifH4R+fQ==
-----END PUBLIC KEY-----
The question is: how to I get this into a .env file, and have it loaded properly as an environment variable? My attempts so far have failed.

I tried:

PUBLIC_KEY="-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEMF802GSVwt2ZsFlmYR6Yy4rzZR8A
o5XaElze2V5JBjeT4fUnGrK0mjvYK/CTaCVHTwq8QsC1osfN7OifH4R+fQ==
-----END PUBLIC KEY-----"
PUBLIC_KEY="-----BEGIN PUBLIC KEY-----\nMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEMF802GSVwt2ZsFlmYR6Yy4rzZR8A\no5XaElze2V5JBjeT4fUnGrK0mjvYK/CTaCVHTwq8QsC1osfN7OifH4R+fQ==\n-----END PUBLIC KEY-----"
and the same as above, but with single quotes.

None of these seem to do the trick.

I ended up base64 encoding the key, and decoding it on runtime, but that just seems like a workaround, not a proper solution.