feat(ssh-agent): add `ssh-add-args` setting (#7908)

* ssh-agent: add `:omz:plugins:ssh-agent ssh_add_args` option

* Clean up and document extra setting

* Document valid ssh-add arguments
Co-authored-by: Marc Cornellà <hello@mcornella.com>

plugins/ssh-agent/README.md

@@ -9,7 +9,7 @@ To enable it, add `ssh-agent` to your plugins:
 plugins=(... ssh-agent)
 ```
 
-## Instructions
+## Settings
 
 **IMPORTANT: put these settings _before_ the line that sources oh-my-zsh**
 
@@ -19,12 +19,16 @@ To enable **agent forwarding support** add the following to your zshrc file:
 zstyle :omz:plugins:ssh-agent agent-forwarding on
 ```
 
+----
+
 To **load multiple identities** use the `identities` style, For example:
 
 ```zsh
 zstyle :omz:plugins:ssh-agent identities id_rsa id_rsa2 id_github
 ```
 
+----
+
 To **set the maximum lifetime of the identities**, use the `lifetime` style.
 The lifetime may be specified in seconds or as described in sshd_config(5)
 (see _TIME FORMATS_). If left unspecified, the default lifetime is forever.
@@ -33,6 +37,24 @@ The lifetime may be specified in seconds or as described in sshd_config(5)
 zstyle :omz:plugins:ssh-agent lifetime 4h
 ```
 
+----
+
+To **pass arguments to the `ssh-add` command** that adds the identities on startup,
+use the `ssh-add-args` setting. You can pass multiple arguments separated by spaces:
+
+```zsh
+zstyle :omz:plugins:ssh-agent ssh-add-args -K -c -a /run/user/1000/ssh-auth
+```
+
+These will then be passed the the `ssh-add` call as if written directly. The example
+above will turn into:
+
+```zsh
+ssh-add -K -c -a /run/user/1000/ssh-auth <identities>
+```
+
+For valid `ssh-add` arguments run `ssh-add --help` or `man ssh-add`.
+
 ## Credits
 
 Based on code from Joseph M. Reagle: https://www.cygwin.com/ml/cygwin/2001-06/msg00537.html

plugins/ssh-agent/ssh-agent.plugin.zsh

@@ -48,7 +48,9 @@ function _add_identities() {
 		fi
 	done
 
-	[[ -n "$not_loaded" ]] && ssh-add ${^not_loaded}
+	local args
+	zstyle -a :omz:plugins:ssh-agent ssh-add-args args
+	[[ -n "$not_loaded" ]] && ssh-add "${args[@]}" ${^not_loaded}
 }
 
 # Get the filename to store/lookup the environment from