opgpcard: Add a parameter '--key-only' to the ssh command.

This outputs only one line, containing the ssh public key string, which is useful in scripts (e.g. in CI).

tools/src/commands/ssh.rs

@@ -22,6 +22,9 @@ pub struct SshCommand {
         help = "Identifier of the card to use"
     )]
     pub ident: Option<String>,
+
+    #[clap(long, help = "Only print the ssh public key")]
+    pub key_only: bool,
 }
 
 pub fn print_ssh(
@@ -31,6 +34,8 @@ pub fn print_ssh(
 ) -> Result<()> {
     let mut output = output::Ssh::default();
 
+    output.key_only(command.key_only);
+
     let ident = command.ident;
 
     let backend = pick_card_for_reading(ident)?;

tools/src/output/ssh.rs

@@ -8,12 +8,17 @@ use crate::{OutputBuilder, OutputFormat, OutputVariant, OutputVersion};
 
 #[derive(Debug, Default, Serialize)]
 pub struct Ssh {
+    key_only: bool, // only print ssh public key, in text mode
     ident: String,
     authentication_key_fingerprint: Option<String>,
     ssh_public_key: Option<String>,
 }
 
 impl Ssh {
+    pub fn key_only(&mut self, ssh_key_only: bool) {
+        self.key_only = ssh_key_only;
+    }
+
     pub fn ident(&mut self, ident: String) {
         self.ident = ident;
     }
@@ -27,6 +32,7 @@ impl Ssh {
     }
 
     fn text(&self) -> Result<String, OpgpCardError> {
+        if !self.key_only {
             let mut s = format!("OpenPGP card {}\n\n", self.ident);
 
             if let Some(fp) = &self.authentication_key_fingerprint {
@@ -37,6 +43,9 @@ impl Ssh {
             }
 
             Ok(s)
+        } else {
+            Ok(self.ssh_public_key.clone().unwrap_or("".to_string()))
+        }
     }
 
     fn v1(&self) -> Result<SshV0, OpgpCardError> {