+This is a unix like password store (`/etc/pve/priv/shadow.cfg`).
+Password are encrypted using the SHA-256 hash method.
+This is the most convenient method for small (or even medium)
+installations where users do not need access to anything outside of
+{pve}. In this case users are fully managed by {pve} and are able to
+change their own passwords via the GUI.
+
+LDAP::
+It is possible to authenticate users via an LDAP server (e.g.
+openldap). The server and an optional fallback server can be
+configured and the connection can be encrypted via SSL.
++
+Users are searched under a 'Base Domain Name' (`base_dn`), with the
+user name found in the attribute specified in the 'User Attribute Name'
+(`user_attr`) field.
++
+For instance, if a user is represented via the
+following ldif dataset:
++
+----
+# user1 of People at ldap-test.com
+dn: uid=user1,ou=People,dc=ldap-test,dc=com
+objectClass: top
+objectClass: person
+objectClass: organizationalPerson
+objectClass: inetOrgPerson
+uid: user1
+cn: Test User 1
+sn: Testers
+description: This is the first test user.
+----
++
+The 'Base Domain Name' would be `ou=People,dc=ldap-test,dc=com` and the user
+attribute would be `uid`.
++
+If {pve} needs to authenticate (bind) to the ldap server before being
+able to query and authenticate users, a bind domain name can be
+configured via the `bind_dn` property in `/etc/pve/domains.cfg`. Its
+password then has to be stored in `/etc/pve/priv/ldap/<realmname>.pw`
+(e.g. `/etc/pve/priv/ldap/my-ldap.pw`). This file should contain a
+single line containing the raw password.
++
+To verify certificates, you need to to set `capath`. You can set it either
+directly to the CA certificate of your LDAP server, or to the system path
+containing all trusted CA certificates (`/etc/ssl/certs`).
+Additionally, you need to set the `verify` option, which can also be doen over
+the web interface.
+
+Microsoft Active Directory::
+
+A server and authentication domain need to be specified. Like with
+ldap an optional fallback server, optional port, and SSL
+encryption can be configured.
+
+[[pveum_ldap_sync]]
+Syncing LDAP-based realms
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+[thumbnail="screenshot/gui-datacenter-realm-add-ldap.png"]
+
+It is possible to sync users and groups for LDAP based realms. You can use the
+CLI command
+
+----
+ pveum realm sync <realm>
+----
+or in the `Authentication` panel of the GUI. Users and groups are synced to the
+cluster-wide user configuration file `/etc/pve/user.cfg`.
+
+Requirements and limitations
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The `bind_dn` is used to query the users and groups. This account needs access
+to all desired entries.
+
+The fields which represent the names of the users and groups can be configured
+via the `user_attr` and `group_name_attr` respectively. Only entries which
+adhere to the usual character limitations of the user.cfg are synced.
+
+Groups are synced with `-$realm` attached to the name, to avoid naming
+conflicts. Please make sure that a sync does not overwrite manually created
+groups.
+
+[[pveum_ldap_sync_options]]
+Options
+^^^^^^^
+
+[thumbnail="screenshot/gui-datacenter-realm-add-ldap-sync-options.png"]
+
+The main options for syncing are:
+
+* `dry-run`: No data is written to the config. This is useful if you want to
+ see which users and groups would get synced to the user.cfg. This is set
+ when you click `Preview` in the GUI.
+
+* `enable-new`: If set, the newly synced users are enabled and can login.
+ The default is `true`.
+
+* `full`: If set, the sync uses the LDAP Directory as a source of truth,
+ overwriting information set manually in the user.cfg and deletes users
+ and groups which are not present in the LDAP directory. If not set,
+ only new data is written to the config, and no stale users are deleted.
+
+* `purge`: If set, sync removes all corresponding ACLs when removing users
+ and groups. This is only useful with the option `full`.
+
+* `scope`: The scope of what to sync. It can be either `users`, `groups` or
+ `both`.
+
+These options are either set as parameters or as defaults, via the
+realm option `sync-defaults-options`.
+
+[[pveum_tfa_auth]]
+Two-factor authentication
+-------------------------
+
+There are two ways to use two-factor authentication:
+
+It can be required by the authentication realm, either via 'TOTP'
+(Time-based One-Time Password) or 'YubiKey OTP'. In this case a newly
+created user needs their keys added immediately as there is no way to
+log in without the second factor. In the case of 'TOTP', users can
+also change the 'TOTP' later on, provided they can log in first.
+
+Alternatively, users can choose to opt in to two-factor authentication
+via 'TOTP' later on, even if the realm does not enforce it. As another
+option, if the server has an 'AppId' configured, a user can opt into
+'U2F' authentication, provided the realm does not enforce any other
+second factor.
+
+Realm enforced two-factor authentication
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This can be done by selecting one of the available methods via the
+'TFA' dropdown box when adding or editing an Authentication Realm.
+When a realm has TFA enabled it becomes a requirement and only users
+with configured TFA will be able to login.
+
+Currently there are two methods available:
+
+Time-based OATH (TOTP):: This uses the standard HMAC-SHA1 algorithm
+where the current time is hashed with the user's configured key. The
+time step and password length parameters are configured.
++
+A user can have multiple keys configured (separated by spaces), and the keys
+can be specified in Base32 (RFC3548) or hexadecimal notation.
++
+{pve} provides a key generation tool (`oathkeygen`) which prints out a random
+key in Base32 notation which can be used directly with various OTP tools, such
+as the `oathtool` command line tool, or on Android Google Authenticator,
+FreeOTP, andOTP or similar applications.
+
+YubiKey OTP::
+For authenticating via a YubiKey a Yubico API ID, API KEY and validation
+server URL must be configured, and users must have a YubiKey available. In
+order to get the key ID from a YubiKey, you can trigger the YubiKey once
+after connecting it to USB and copy the first 12 characters of the typed
+password into the user's 'Key IDs' field.
+
++
+Please refer to the https://developers.yubico.com/OTP/[YubiKey OTP]
+documentation for how to use the
+https://www.yubico.com/products/services-software/yubicloud/[YubiCloud] or
+https://developers.yubico.com/Software_Projects/Yubico_OTP/YubiCloud_Validation_Servers/[host
+your own verification server].
+
+[[pveum_user_configured_totp]]
+User configured TOTP authentication
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Users can choose to enable 'TOTP' as a second factor on login via the 'TFA'
+button in the user list (unless the realm enforces 'YubiKey OTP').
+
+[thumbnail="screenshot/gui-datacenter-users-tfa.png"]
+
+After opening the 'TFA' window, the user is presented with a dialog to setup
+'TOTP' authentication. The 'Secret' field contains the key, which can simply be
+generated randomly via the 'Randomize' button. An optional 'Issuer Name' can be
+added to provide information to the 'TOTP' app what the key belongs to.
+Most 'TOTP' apps will show the issuer name together with the corresponding
+'OTP' values. The user name is also included in the QR code for the 'TOTP' app.
+
+After generating a key, a QR code will be displayed which can be used with most
+OTP apps such as FreeOTP. Now the user needs to verify both the current user
+password (unless logged in as 'root'), as well as the ability to correctly use
+the 'TOTP' key by typing the current 'OTP' value into the 'Verification Code'
+field before pressing the 'Apply' button.
+
+[[pveum_configure_u2f]]
+Server side U2F configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To allow users to use 'U2F' authentication, the server needs to have a valid
+domain with a valid https certificate. Initially an 'AppId'
+footnote:[AppId https://developers.yubico.com/U2F/App_ID.html]
+needs to be configured.
+
+NOTE: Changing the 'AppId' will render all existing 'U2F' registrations
+unusable!
+
+This is done via `/etc/pve/datacenter.cfg`, for instance:
+
+----
+u2f: appid=https://mypve.example.com:8006
+----
+
+For a single node, the 'AppId' can simply be the web UI address exactly as it
+is used in the browser, including the 'https://' and the port as shown above.
+Please note that some browsers may be more strict than others when matching
+'AppIds'.
+
+When using multiple nodes, it is best to have a separate `https` server
+providing an `appid.json`
+footnote:[Multi-facet apps: https://developers.yubico.com/U2F/App_ID.html]
+file, as it seems to be compatible with most
+browsers. If all nodes use subdomains of the same top level domain, it may be
+enough to use the TLD as 'AppId', but note that some browsers may not accept
+this.
+
+NOTE: A bad 'AppId' will usually produce an error, but we have encountered
+situation where this does not happen, particularly when using a top level domain
+'AppId' for a node accessed via a subdomain in Chromium. For this reason it is
+recommended to test the configuration with multiple browsers, as changing the
+'AppId' later will render existing 'U2F' registrations unusable.
+
+[[pveum_user_configured_u2f]]
+Activating U2F as a user
+~~~~~~~~~~~~~~~~~~~~~~~~