Add doc comment with example to AllowedSigner

Author: SRv6d

src/allowed_signers.rs

@@ -26,6 +26,22 @@ impl AllowedSigner {
 }
 
 impl fmt::Display for AllowedSigner {
+    /// Display the allowed signer in the format expected by the `allowed_signers` file.
+    ///
+    /// # Examples
+    /// ```
+    /// # use hanko::AllowedSigner;
+    /// # use chrono::{TimeZone, Local};
+    /// let signer = AllowedSigner {
+    ///     principal: "cwoods@universal.exports".to_string(),
+    ///     valid_after: None,
+    ///     valid_before: Some(Local.with_ymd_and_hms(2030, 1, 1, 0, 0, 0).unwrap()),
+    ///     key: "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIJHDGMF+tZQL3dcr1arPst+YP8v33Is0kAJVvyTKrxMw"
+    ///         .parse()
+    ///         .unwrap(),
+    /// };
+    /// assert_eq!(signer.to_string(), "cwoods@universal.exports valid-before=20300101000000 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIJHDGMF+tZQL3dcr1arPst+YP8v33Is0kAJVvyTKrxMw");
+    /// ```
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{}", self.principal)?;