The `sshca user login` command will eventually provide the command-line
interface for obtaining user SSH certificates. It initiates the OAuth2
login process, retreiving an OpenID Connect Identity Token from the
OpenID Server. This token will be submitted to the SSHCA server to
authorize a request to sign a certificate. For now, though, the token
is printed to standard output, e.g. to be used in a `curl` request.
Dustin
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