ssh-agent: improvements (#6309)

* ssh-agent: lock this script with a mkdir style mutex

This script is a kind of singleton pattern and is not reentrant.
If several shells are oppened in a fast sequence, then several
independent ssh-agents would be created, which is not acceptable.
A mutex is required.

Signed-off-by: Nuno Goncalves <nunojpg@gmail.com>

* ssh-agent: only start agent if .ssh dir exists

To use the same profile system-wide, it might happen
that the .ssh directory does not exist
(typically $HOME/.ssh/). This would trigger a error.

Creating the directory would be a option, but it
usually will not make sense to do so because it means
the user doesn't have ssh keys or config.

Signed-off-by: Nuno Goncalves <nunojpg@gmail.com>

* ssh-agent: adds lazy option to disable key loading on start

Option is documented on updated README.md

Signed-off-by: Nuno Goncalves <nunojpg@gmail.com>

* ssh-agent: simplify agent-forwarding checking

Signed-off-by: Nuno Goncalves <nunojpg@gmail.com>

Co-authored-by: Robby Russell <robby@planetargon.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/plugins/ssh-agent/README.md b/plugins/ssh-agent/README.md
index 8765a9c7e..aa96f9cc9 100644
--- a/plugins/ssh-agent/README.md
+++ b/plugins/ssh-agent/README.md
@@ -19,9 +19,17 @@ To enable **agent forwarding support** add the following to your zshrc file:
 zstyle :omz:plugins:ssh-agent agent-forwarding on
 ```
 
-----
+To **NOT load any identities on start** use the `lazy` style.
+This is particularly usefull when combined with the AddKeysToAgent
+(available from OpenSSH 7.2), since it allows to enter the password only
+on first use.
+
+```zsh
+zstyle :omz:plugins:ssh-agent lazy yes
+```
 
-To **load multiple identities** use the `identities` style, For example:
+To **load multiple identities** use the `identities` style. This have no
+effect if `lazy` is enabled.
 
 ```zsh
 zstyle :omz:plugins:ssh-agent identities id_rsa id_rsa2 id_github