♻️ Simplify SASL::{Name}Authenticator registration

Author: nevans

lib/net/imap/sasl/authenticators.rb

@@ -30,9 +30,15 @@ def authenticators; @authenticators.dup end
     #
     # See PlainAuthenticator, XOauth2Authenticator, and DigestMD5Authenticator for
     # examples.
-    def add_authenticator(mechanism, authenticator, warn_overwrite: true)
+    def add_authenticator(mechanism, authenticator = nil, warn_overwrite: true)
       mechanism = mechanism.to_str
       upcased = mechanism.upcase
+      authenticator ||= ->(*creds, **props, &block) {
+        class_name    = "#{mechanism.gsub(/-/, "")}Authenticator"
+        auth_class = Net::IMAP::SASL.const_get(class_name.to_sym)
+        add_authenticator(upcased, auth_class, warn_overwrite: false)
+        auth_class.new(*creds, **props, &block)
+      }
       if warn_overwrite && (original = authenticators[upcased])
         warn("%p: replacing %p authenticator: %p" % [ self, upcased, original],
              uplevel: 1)