bug#54127: 29.0.50; auth-sources defcustom bug

[Mauro Aranda]

After emacs -Q:

M-x load-library RET auth-source
M-x customize-option RET auth-sources
Click the INS button to insert a new source.
Select "Source definition" from the Value Menu.
Click the INS button for Extra Parameters.

A new extra parameter is added but with an invalid value, detected by
the widget code.

Furthermore, auth-source-backend-parse-parameters thinks these extra
parameters are in a plist, but the type spec looks wrong in that case
since after setting for the session, auth-sources is something like:
("~/.authinfo" "~/.authinfo.gpg" "~/.netrc"
 (:source ""
          (:host t)
          (:port imap)))


In GNU Emacs 29.0.50 (build 66, i686-pc-linux-gnu, GTK+ Version 2.24.32, cairo 
version 1.16.0)
 of 2022-02-23 built on tbb-desktop
Repository revision: 85ad8616007e286c237bb2906d1928bb551462e7
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Ubuntu 18.04.6 LTS

Configured using:
 'configure --with-dbus --with-mailutils
 PKG_CONFIG_PATH=/opt/cairo/lib/pkgconfig'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG MODULES
NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM GTK2 ZLIB

Important settings:
  value of $LC_MONETARY: es_AR.UTF-8
  value of $LC_NUMERIC: es_AR.UTF-8
  value of $LC_TIME: es_AR.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media rmc puny
dired dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068 epg-config gnus-util text-property-search time-date seq gv
subr-x byte-opt bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax font-core term/tty-colors frame minibuffer cl-generic
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget keymap hashtable-print-readable backquote threads
dbusbind inotify dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 8 42511 5795)
 (symbols 24 5665 1)
 (strings 16 15717 1167)
 (string-bytes 1 503805)
 (vectors 8 11122)
 (vector-slots 4 164043 34266)
 (floats 8 20 26)
 (intervals 28 202 0)
 (buffers 564 10))