This implements a fairly loose validation of the public key format.
It does not check specific key types, nor try to decode the base64
key and check it for validity. It does check that the format in
general is valid, and that at least one valid key is present.
It will reject public keys, because those don't have a space.
This requires changes to many specs to have them use a valid public
key format. In many cases, that is done by changing a single
dash to a space.
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