/usr/share/augeas/lenses/dist/passwd.aug is in augeas-lenses 1.10.1-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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 Module: Passwd
 Parses /etc/passwd
 Author: Free Ekanayaka <free@64studio.com>
 About: Reference
        - man 5 passwd
        - man 3 getpwnam
 Each line in the unix passwd file represents a single user record, whose
 colon-separated attributes correspond to the members of the passwd struct
*)
module Passwd =
   autoload xfm
(************************************************************************
 * Group:                    USEFUL PRIMITIVES
 *************************************************************************)
(* Group: Comments and empty lines *)
let eol        = Util.eol
let comment    = Util.comment
let empty      = Util.empty
let dels       = Util.del_str
let word       = Rx.word
let integer    = Rx.integer
let colon      = Sep.colon
let sto_to_eol = store Rx.space_in
let sto_to_col = store /[^:\r\n]+/
(* Store an empty string if nothing matches *)
let sto_to_col_or_empty = store /[^:\r\n]*/
(************************************************************************
 * Group:                        ENTRIES
 *************************************************************************)
let username  = /[_.A-Za-z0-9][-_.A-Za-z0-9]*\$?/
(* View: password
        pw_passwd *)
let password  = [ label "password" . sto_to_col?   . colon ]
(* View: uid
        pw_uid *)
let uid       = [ label "uid"      . store integer . colon ]
(* View: gid
        pw_gid *)
let gid       = [ label "gid"      . store integer . colon ]
(* View: name
        pw_gecos; the user's full name *)
let name      = [ label "name"     . sto_to_col? . colon ]
(* View: home
        pw_dir *)
let home      = [ label "home"     . sto_to_col?   . colon ]
(* View: shell
        pw_shell *)
let shell     = [ label "shell"    . sto_to_eol? ]
(* View: entry
        struct passwd *)
let entry     = [ key username
                . colon
                . password
                . uid
                . gid
                . name
                . home
                . shell
                . eol ]
(* NIS entries *)
let niscommon =  [ label "password" . sto_to_col ]?    . colon
               . [ label "uid"      . store integer ]? . colon
               . [ label "gid"      . store integer ]? . colon
               . [ label "name"     . sto_to_col ]?    . colon
               . [ label "home"     . sto_to_col ]?    . colon
               . [ label "shell"    . sto_to_eol ]?
let nisentry =
  let overrides =
        colon
      . niscommon in
  [ dels "+@" . label "@nis" . store username . overrides . eol ]
let nisuserplus =
  let overrides =
        colon
      . niscommon in
  [ dels "+" . label "@+nisuser" . store username . overrides . eol ]
let nisuserminus =
  let overrides =
        colon
      . niscommon in
  [ dels "-" . label "@-nisuser" . store username . overrides . eol ]
let nisdefault =
  let overrides =
        colon
      . [ label "password" . sto_to_col_or_empty . colon ]
      . [ label "uid"      . store integer? . colon ]
      . [ label "gid"      . store integer? . colon ]
      . [ label "name"     . sto_to_col?    . colon ]
      . [ label "home"     . sto_to_col?    . colon ]
      . [ label "shell"    . sto_to_eol? ] in
  [ dels "+" . label "@nisdefault" . overrides? . eol ]
(************************************************************************
 *                                LENS
 *************************************************************************)
let lns        = (comment|empty|entry|nisentry|nisdefault|nisuserplus|nisuserminus) *
let filter     = incl "/etc/passwd"
let xfm        = transform lns filter
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