machine: hetzner: Allow connections using ssh-agent.

* gnu/machine/hetzner.scm (<hetzner-configuration>): Add ssh-public-key.
* doc/guix.texi (System Configuration)[hetzner-configuration]: Document it.

Change-Id: I7354ead508b1a4819534c6b22ba1f089749927c2
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Modified-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -46014,9 +46014,14 @@ equivalent.  Other server types and their current prices can be found
 server type is currently not supported, since its rescue system is too
 small to bootstrap a Guix system from.
 
-@item @code{ssh-key}
+@item @code{ssh-key} (default: @code{#f})
-The file name of the SSH private key to use to authenticate with the
+If specified, the file name of the SSH private key to use to
-remote host.
+authenticate with the remote host.
+
+@item @code{ssh-public-key} (default: extracted from @code{ssh-key})
+If specified, either a public key as returned by
+@code{string->public-key} or the path to the SSH public key to use to
+authenticate with the remote host.
 
 @end table
 
@@ -46080,7 +46085,7 @@ shared vCPUs and 32 GB of RAM on the @code{x86_64} architecture.
        (environment hetzner-environment-type)
        (configuration (hetzner-configuration
                        (server-type "cpx51")
-                       (ssh-key "/home/charlie/.ssh/id_rsa")))))
+                       (ssh-public-key "/home/charlie/.ssh/id_rsa.pub")))))
 @end lisp
 
 @vindex GUIX_HETZNER_API_TOKEN

gnu/machine/hetzner.scm

@@ -77,6 +77,7 @@
             hetzner-configuration-location
             hetzner-configuration-server-type
             hetzner-configuration-ssh-key
+            hetzner-configuration-ssh-public-key
             hetzner-configuration?
             hetzner-environment-type))
 
@@ -204,20 +205,24 @@ Have you run 'guix archive --generate-key'?")
             (default "fsn1"))
   (server-type hetzner-configuration-server-type ; string
                (default "cx42"))
-  (ssh-key hetzner-configuration-ssh-key)) ; string
+  (ssh-public-key hetzner-configuration-ssh-public-key ; public-key | string
+                  (thunked)
+                  (default (public-key-from-file (hetzner-configuration-ssh-key this-hetzner-configuration)))
+                  (sanitize
+                   (lambda (value)
+                     (if (string? value) (public-key-from-file value) value))))
+  (ssh-key hetzner-configuration-ssh-key
+           (default #f))) ; #f | string
 
 (define (hetzner-configuration-ssh-key-fingerprint config)
   "Return the SSH public key fingerprint of CONFIG as a string."
-  (and-let* ((file-name (hetzner-configuration-ssh-key config))
+  (and-let* ((pubkey (hetzner-configuration-ssh-public-key config))
-             (privkey (private-key-from-file file-name))
-             (pubkey (private-key->public-key privkey))
              (hash (get-public-key-hash pubkey 'md5)))
     (bytevector->hex-string hash)))
 
 (define (hetzner-configuration-ssh-key-public config)
   "Return the SSH public key of CONFIG as a string."
-  (and-let* ((ssh-key (hetzner-configuration-ssh-key config))
+  (let ((public-key (hetzner-configuration-ssh-public-key config)))
-             (public-key (public-key-from-file ssh-key)))
     (format #f "ssh-~a ~a" (get-key-type public-key)
             (public-key->string public-key))))