* gnu/services/authentication.scm (pam-ldap-pam-service): Use
'file-append' instead of #~(string-append ...).
* gnu/services/base.scm (greetd-pam-service): Likewise.
* gnu/services/kerberos.scm (pam-krb5-pam-service): Likewise.
* gnu/services/pam-mount.scm (pam-mount-pam-service): Likewise.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

* gnu/system/pam.scm (<pam-extension>): New record type.
(pam-shepherd-service): Add Shepherd synchronization point.

* gnu/services/mail.scm (dovecot-shepherd-service)
* gnu/services/lightdm.scm (lightdm-shepherd-service)
* gnu/services/mail.scm (opensmtpd-shepherd-service)
* gnu/services/sddm.scm (sddm-shepherd-service)
* gnu/services/ssh.scm (lsh-shepherd-service, openssh-shepherd-service)
* gnu/services/xorg.scm (slim-shepherd-service, gdm-shepherd-service)
* gnu/services/base.scm (greetd-shepherd-services): Add PAM requirement.

* gnu/system/pam.scm (/etc-entry, extend-configuration,
pam-root-service-type, pam-root-service)
* gnu/services/authentication.scm (pam-ldap-pam-service)
* gnu/services/base.scm (pam-limits-service-type)
(greetd-pam-service)
* gnu/services/desktop.scm (pam-gnome-keyring)
* gnu/services/kerberos.scm (pam-krb5-pam-service)
* gnu/services/pam-mount.scm (pam-mount-pam-service): Adapt to use
pam-extension.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

Use *unspecified* as a marker for field values that have not been set.

Rationale: 'disabled may easily clash with user values for boolean fields, is
confusing (i.e. its meaning is *not* boolean false, but unspecified) and it
also passes silently through the symbol? predicate of a field of type symbol.

* gnu/services/configuration.scm (configuration-missing-default-value):
Renamed from configuration-no-default-value.
(define-maybe-helper): Use *unspecified* instead of 'disabled, and make
the default value optional.
* gnu/home/services/desktop.scm (home-redshift-configuration):
Change (maybe-xyz 'disabled) to maybe-xyz.
* gnu/services/authentication.scm (nslcd-configuration): Likewise.
* gnu/services/cgit.scm (repository-cgit-configuration): Likewise.
* gnu/services/file-sharing.scm (serialize-maybe-string)
(serialize-maybe-file-object): Use 'unspecified?' instead of (eq? val
'disabled).
* gnu/services/messaging.scm (raw-content?): Likewise.
(ssl-configuration): Change (maybe-xyz 'disabled) to maybe-xyz.
(prosody-configuration): Likewise.
* gnu/services/file-sharing.scm (transmission-daemon-configuration):
Likewise.
* gnu/services/messaging.scm (define-all-configurations):
Use *unspecified* instead of 'disabled'.
* gnu/services/networking.scm (opendht-configuration): Likewise.
* gnu/services/pm.scm (tlp-configuration): Likewise.
* gnu/services/telephony.scm (jami-account): Likewise.
(jami-configuration): Likewise.
* gnu/services/vpn.scm (openvpn-client-configuration): Likewise.
* tests/services/configuration.scm ("maybe type, no default")
("maybe type, with default"): New tests.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

* gnu/services/authentication.scm (fprintd-configuration)
(nslcd-configuration): Substitute file-like objects for package ones.
* gnu/services/cgit.scm (cgit-configuration, opaque-cgit-configuration):
Likewise.
* gnu/services/cups.scm (package-list?, cups-configuration): Likewise.
* gnu/services/dns.scm (verify-knot-configuration)
(ddclient-configuration): Likewise.
* gnu/services/docker.scm (docker-configuration): Likewise.
* gnu/services/file-sharing.scm (transmission-daemon-configuration): Likewise.
* gnu/services/getmail.scm (getmail-configuration): Likewise.
* gnu/services/mail.scm (dovecot-configuration)
(opaque-dovecot-configuration): Likewise.
* gnu/services/messaging.scm (prosody-configuration)
(opaque-prosody-configuration): Likewise.
* gnu/services/monitoring.scm (zabbix-server-configuration)
(zabbix-agent-configuration): Likewise.
* gnu/services/networking.scm (opendht-configuration): Likewise.
* gnu/services/pm.scm (tlp-configuration): Likewise.
* gnu/services/telephony.scm (jami-configuration): Likewise.
* gnu/services/virtualization.scm (libvirt-configuration)
(qemu-guest-agent-configuration): Likewise.
* gnu/services/vpn.scm (openvpn-client-configuration): Likewise.

This addresses a potential security issue, where a compromised
service could trick the activation code in changing the permissions,
owner and group of arbitrary files.  However, this patch is
currently only a partial fix, due to a TOCTTOU (time-of-check to
time-of-use) race, which can be fixed once guile has bindings
to openat and friends.

Fixes: <https://lists.gnu.org/archive/html/guix-devel/2021-01/msg00388.html>

* gnu/build/activation.scm: new procedure 'mkdir-p/perms'.
* gnu/services/authentication.scm
  (%nslcd-activation, nslcd-service-type): use new procedure.
* gnu/services/cups.scm (%cups-activation): likewise.
* gnu/services/dbus.scm (dbus-activation): likewise.
* gnu/services/dns.scm (knot-activation): likewise.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

* gnu/services/authentication.scm (fprintd-service-type)[extensions]: Add
polkit-service-type.

* gnu/services/authentication.scm: Use define-configuration in fprintd.

* gnu/services/authentication.scm (<fprintd-configuration>)[ntp]: Rename to...
[fprintd]: ...this.
(fprintd-dbus-service): New procedure.
(fprintd-service-type): Use it.
[default-value]: Add value.

* gnu/services/authentication.scm (nslcd-service-type, nslcd-configuration,
%nslcd-accounts): New variables.
(uglify-field-name, value->string, serialize-field, serialize-list,
ssl-option?, tls-reqcert-option?, deref-option?,
comma-separated-list-of-strings?, serialize-ignore-users-option, log-option?,
serialize-log-option, valid-map?, scope-option?, serialize-scope-option,
map-entry?, list-of-map-entries?, filter-entry?, list-of-filter-entries?,
serialize-filter-entry, serialize-list-of-filter-entries, serialize-map-entry,
serialize-list-of-map-entries, nslcd-config-file, nslcd-etc-service,
nslcd-shepherd-service, pam-ldap-pam-services, pam-ldap-pam-service,
generate-nslcd-documentation): New procedures.
* gnu/tests/ldap.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* doc/guix.texi (LDAP Services): Document it.

Follow-up to 7f93bbd5aadf0427190769fba8f478c29e37b4f4.

* gnu/services/authentication.scm: Fix module name.