agent/auto-auth: Add min_backoff to set first backoff value (#15204)

* Add initial_backoff to auto-auth method

* Disable retries in client

* Fix bug

* Thread initial backoff to CT

* Add comment

* Change to min_backoff

* changelog

* remove initial references, review

* fix test

* Thread max_backoff through

* Add doc note for max_backoff/templating

command/agent.go

@@ -790,10 +790,19 @@ func (c *AgentCommand) Run(args []string) int {
 	// Start auto-auth and sink servers
 	if method != nil {
 		enableTokenCh := len(config.Templates) > 0
+
+		// Auth Handler is going to set its own retry values, so we want to
+		// work on a copy of the client to not affect other subsystems.
+		clonedClient, err := c.client.Clone()
+		if err != nil {
+			c.UI.Error(fmt.Sprintf("Error cloning client for auth handler: %v", err))
+			return 1
+		}
 		ah := auth.NewAuthHandler(&auth.AuthHandlerConfig{
 			Logger:                       c.logger.Named("auth.handler"),
-			Client:                       c.client,
+			Client:                       clonedClient,
 			WrapTTL:                      config.AutoAuth.Method.WrapTTL,
+			MinBackoff:                   config.AutoAuth.Method.MinBackoff,
 			MaxBackoff:                   config.AutoAuth.Method.MaxBackoff,
 			EnableReauthOnNewCredentials: config.AutoAuth.EnableReauthOnNewCredentials,
 			EnableTemplateTokenCh:        enableTokenCh,