LDAP (RFC 7612) sharing/browsing support

[michaelrsweet]

(Referencing corresponding ippsample sharing and ippsample browsing issues.)

Implement LDAP (RFC 7612) sharing/browsing support in cupsd, with cupsEnumDests using a new CUPS operation to search for shared printers.

Changes include:

• Add OpenLDAP schema (LDIF) file for printers (installed to /etc/openldap/schema)
• Add LDAPBindDN, LDAPPassword, LDAPServer, and LDAPDN directive support to "cupsd.conf"
• Add ldap calls in dirsvc.c
• Add vendor extension operation to cupsd to search for LDAP printers and return a list to clients (locally only). Working name: CUPS-Search-Printers (which could also do the Bonjour lookups as well)
• Add request in cupsEnumDests.

CUPS-Search-Printers request:

Group 1: Operation Attributes:
    "attributes-charset (charset)"
    "attributes-natural-language (naturalLanguage)"
    "printer-uri (uri)" or "system-uri (uri)"
    "requesting-user-name (name)"
    "requested-attributes (1setOf keyword)"
    "limit (integer(1:MAX))"
    "max-time (integer(0:MAX))" - timeout in milliseconds
    "printer-location (text)"
    "printer-type (enum)"
    "printer-type-mask (enum)"
    "printer-uuid (uri)"

CUPS-Search-Printers response:

Group 1: Operation Attributes:
    "attributes-charset (charset)"
    "attributes-natural-language (naturalLanguage)"

Groups 2-N: Printer Attributes:
    Printer attributes as defined in [Appendix D of RFC 8011](https://tools.ietf.org/html/rfc8011#appendix-D)

Example cupsd.conf directives:

LDAPBindDN uid=cupsd,ou=people,dc=example,dc=org
LDAPPassword <ldap password>
LDAPServer ldaps://ldap-server.example.org/
LDAPDN dc=example,dc=org

[michaelrsweet]

This no longer seems likely.