# Set up LDAP authentication and authorization using NativeLDAP

This document describes an example configuration of LDAP authentication and authorization using direct binding to an LDAP server (Native LDAP). We recommend testing this setup in a non-production environment first, before applying it in production.

## Assumptions

1. The setup of an LDAP server is out of scope of this document. We assume that you are familiar with the LDAP server schema.

2. You have the LDAP server up and running and it is accessible to the servers with Percona Server for MongoDB installed.

3. This document primarily focuses on OpenLDAP used as the LDAP server and the examples are given based on the OpenLDAP format. If you are using Active Directory, refer to the [Active Directory configuration](#active-directory-configuration) section.

4. You have the `sudo` privilege to the server with the Percona Server for MongoDB installed.

## Prerequisites

* In this setup we use anonymous binds to the LDAP server. If your LDAP server disallows anonymous binds, create the user that Percona Server for MongoDB will use to connect to and query the LDAP server. Define this user’s credentials for the `security.ldap.bind.queryUser` and `security.ldap.bind.queryPassword`  parameters in the `mongod.conf` configuration file.


* In this setup, we use the following OpenLDAP groups:

```text
dn: cn=testusers,dc=percona,dc=com
objectClass: groupOfNames
cn: testusers
member: cn=alice,dc=percona,dc=com

dn: cn=otherusers,dc=percona,dc=com
objectClass: groupOfNames
cn: otherusers
member: cn=bob,dc=percona,dc=com
```

## Setup procedure

### Configure TLS/SSL connection for Percona Server for MongoDB

By default, Percona Server for MongoDB establishes the TLS connection when binding to the LDAP server and thus, it requires access to the LDAP  certificates. To make Percona Server for MongoDB aware of the certificates, do the following:

1. Place the certificate in the `certs` directory. The path to the `certs` directory is:

    * On Debian / Ubuntu: `/etc/ssl/certs/`

    * On RHEL / CentOS: `/etc/openldap/certs/`

2. Specify the path to the certificates in the `ldap.conf` file:

    === "Debian / Ubuntu"

         ```
         tee -a /etc/openldap/ldap.conf <<EOF
         TLS_CACERT /etc/ssl/certs/my_CA.crt
         EOF
         ```

    === "RHEL and derivatives"

         ```
         tee -a /etc/openldap/ldap.conf <<EOF
         TLS_CACERT /etc/openldap/certs/my_CA.crt
         EOF
         ```

### Create roles for LDAP groups in Percona Server for MongoDB

Percona Server for MongoDB authorizes users based on LDAP group membership. For every group, you must create the role in the `admin` database with the name that exactly matches the  of the LDAP group.

Percona Server for MongoDB maps the user’s LDAP group to the roles and determines what role is assigned to the user. Percona Server for MongoDB then grants privileges defined by this role.

To create the roles, use the following command:

```javascript
var admin = db.getSiblingDB("admin")
db.createRole(
   {
     role: "cn=testusers,dc=percona,dc=com",
     privileges: [],
     roles: [ "readWrite"]
   }
)

db.createRole(
   {
     role: "cn=otherusers,dc=percona,dc=com",
     privileges: [],
     roles: [ "read"]
   }
)
```

### Percona Server for MongoDB configuration

#### Access without username transformation

This section assumes that users connect to Percona Server for MongoDB by providing their LDAP DN as the username.


1. Edit the Percona Server for MongoDB configuration file (by default, `/etc/mongod.conf`) and specify the following configuration:

    ```yaml
    security:
      authorization: "enabled"
      ldap:
        servers: "ldap.example.com"
        transportSecurity: tls
        authz:
           queryTemplate: "dc=percona,dc=com??sub?(&(objectClass=groupOfNames)(member={PROVIDED_USER}))"

    setParameter:
      authenticationMechanisms: "PLAIN"
    ```

    The `{PROVIDED_USER}` variable substitutes the provided username before authentication or username transformation takes place.

    Replace `ldap.example.com` with the hostname of your LDAP server. In the LDAP query template, replace the domain controllers `percona` and `com` with those relevant to your organization.


2. Restart the `mongod` service:

    ```{.bash data-prompt="$"}
    $ sudo systemctl restart mongod
    ```


3. Test the access to Percona Server for MongoDB:

    ```{.bash data-prompt="$"}
    $ mongosh -u "cn=alice,dc=percona,dc=com" -p "secretpwd" --authenticationDatabase '$external' --authenticationMechanism 'PLAIN'
    ```

#### Access with username transformation

If users connect to Percona Server for MongoDB with usernames that are not LDAP , you need to transform these usernames to be accepted by the LDAP server.

Using the `--ldapUserToDNMapping` configuration parameter allows you to do this. You specify the match pattern as a regexp to capture a username. Next, specify how to transform it - either to use a substitution value or to query the LDAP server for a username.

If you don’t know what the substitution or LDAP query string should be, please consult with the LDAP administrators to figure this out.

Note that you can use only the `query` or the `substitution` stage, the combination of two is not allowed.

=== "Substitution"

     1. Edit the Percona Server for MongoDB configuration file (by default, `/etc/mongod.conf`) and specify the `userToDNMapping` parameter:

         ```yaml
         security:
           authorization: "enabled"
           ldap:
             servers: "ldap.example.com"
             transportSecurity: tls
             authz:
                queryTemplate: "dc=percona,dc=com??sub?(&(objectClass=groupOfNames)(member={USER}))"
             userToDNMapping: >-
                   [
                     {
                       match: "([^@]+)@percona\\.com",
                       substitution: "CN={0},DC=percona,DC=com"
                     }
                   ]

         setParameter:
           authenticationMechanisms: "PLAIN"
         ```

         The `{USER}` variable substitutes the username transformed during the `userToDNMapping` stage.

         Modify the given example configuration to match your deployment.

     2. Restart the `mongod` service:

         ```{.bash data-prompt="$"}
         $ sudo systemctl restart mongod
         ```  
     3. Test the access to Percona Server for MongoDB:

         ```{.bash data-prompt="$"}
         $ mongosh -u "alice@percona.com" -p "secretpwd" --authenticationDatabase '$external' --authenticationMechanism 'PLAIN'
         ```

=== "LDAP query"
    
     1. Edit the Percona Server for MongoDB configuration file (by default, `/etc/mongod.conf`) and specify the `userToDNMapping` parameter:

         ```yaml
         security:
           authorization: "enabled"
           ldap:
             servers: "ldap.example.com"
             transportSecurity: tls
             authz:
                queryTemplate: "dc=percona,dc=com??sub?(&(objectClass=groupOfNames)(member={USER}))"
             userToDNMapping: >-
                   [
                     {
                       match: "([^@]+)@percona\\.com",
                       ldapQuery: "dc=percona,dc=com??sub?(&(objectClass=organizationalPerson)(cn={0}))"
                     }
                   ]

         setParameter:
           authenticationMechanisms: "PLAIN"
         ```
        
         The `{USER}` variable substitutes the username transformed during the userToDNMapping stage.

         Modify the given example configuration to match your deployment, For example, replace `ldap.example.com` with the hostname of your LDAP server. Replace the domain controllers (DC) `percona` and `com` with those relevant to your organization. Depending on your LDAP schema, further modifications of the LDAP query may be required.

     2. Restart the `mongod` service:

         ```{.bash data-prompt="$"}
         $ sudo systemctl restart mongod
         ```  

     3. Test the access to Percona Server for MongoDB:

         ```{.bash data-prompt="$"}
         mongosh -u "alice" -p "secretpwd" --authenticationDatabase '$external' --authenticationMechanism 'PLAIN'
         ```

### Active Directory configuration

Microsoft Active Directory uses a different schema for user and group definition. To illustrate Percona Server for MongoDB configuration, we will use the following AD users:

```text
dn:CN=alice,CN=Users,DC=testusers,DC=percona,DC=com
userPrincipalName: alice@testusers.percona.com
memberOf: CN=testusers,CN=Users,DC=percona,DC=com

dn:CN=bob,CN=Users,DC=otherusers,DC=percona,DC=com
userPrincipalName: bob@otherusers.percona.com
memberOf: CN=otherusers,CN=Users,DC=percona,DC=com
```

The following are respective  groups:

```text
dn:CN=testusers,CN=Users,DC=percona,DC=com
member:CN=alice,CN=Users,DC=testusers,DC=example,DC=com

dn:CN=otherusers,CN=Users,DC=percona,DC=com
member:CN=bob,CN=Users,DC=otherusers,DC=example,DC=com
```

Use one of the given Percona Server for MongoDB configurations for user authentication and authorization in Active Directory:

=== "No username transformation"

     1. Edit the `/etc/mongod.conf` configuration file:

         ```yaml
         ldap:
           servers: "ldap.example.com"
           authz:
             queryTemplate: "DC=percona,DC=com??sub?(&(objectClass=group)(member:1.2.840.113556.1.4.1941:={PROVIDED_USER}))"

           setParameter:
             authenticationMechanisms: "PLAIN"
         ```

     2. Restart the `mongod` service:

         ```{.bash data-prompt="$"}
         $ sudo systemctl restart mongod
         ```  

     3. Test the access to Percona Server for MongoDB:

         ```{.bash data-prompt="$"}
         $ mongosh -u "CN=alice,CN=Users,DC=testusers,DC=percona,DC=com" -p "secretpwd" --authenticationDatabase '$external' --authenticationMechanism 'PLAIN'
         ```

=== "Username substitution"

     1. Edit the `/etc/mongod.conf` configuration file:

         ```yaml
         ldap:
           servers: "ldap.example.com"
           authz:
             queryTemplate: "DC=percona,DC=com??sub?(&(objectClass=group)(member:1.2.840.113556.1.4.1941:={USER}))"
           userToDNMapping: >-
                 [
                   {
                     match: "([^@]+)@([^\\.]+)\\.percona\\.com",
                     substitution: "CN={0},CN=Users,DC={1},DC=percona,DC=com"
                   }
                 ]

           setParameter:
             authenticationMechanisms: "PLAIN"
         ```

     2. Restart the `mongod` service:

         ```{.bash data-prompt="$"}
         $ sudo systemctl restart mongod
         ```  

     3. Test the access to Percona Server for MongoDB:

         ```{.bash data-prompt="$"}
         $ mongosh -u "alice@percona.com" -p "secretpwd" --authenticationDatabase '$external' --authenticationMechanism 'PLAIN'
         ```

=== "LDAP query"

     1. Edit the `/etc/mongod.conf` configuration file:

         ```yaml
         ldap:
           servers: "ldap.example.com"
           authz:
             queryTemplate: "DC=percona,DC=com??sub?(&(objectClass=group)(member:1.2.840.113556.1.4.1941:={USER}))"
           userToDNMapping: >-
                 [
                   {
                     match: "(.+)",
                     ldapQuery: "dc=example,dc=com??sub?(&(objectClass=organizationalPerson)(userPrincipalName={0}))"
                   }
                 ]

           setParameter:
             authenticationMechanisms: "PLAIN"
         ```

     2. Restart the `mongod` service:

         ```{.bash data-prompt="$"}
         $ sudo systemctl restart mongod
         ```  

     3. Test the access to Percona Server for MongoDB:

         ```{.bash data-prompt="$"}
         $ mongosh -u "alice" -p "secretpwd" --authenticationDatabase '$external' --authenticationMechanism 'PLAIN'
         ```

Modify one of this example configuration to match your deployment.

!!! admonition ""
    
    This document is based on the following posts from Percona Database Performance Blog:

    * [Percona Server for MongoDB LDAP Enhancements: User-to-DN Mapping](https://www.percona.com/blog/2020/04/24/percona-server-for-mongodb-ldap-enhancements-user-to-dn-mapping/) by Igor Solodovnikov
    * [Authenticate Percona Server for MongoDB Users via Native LDAP](https://www.percona.com/blog/2021/07/08/authenticate-percona-server-for-mongodb-users-via-native-ldap/) by Ivan Groenewold

*[DN]: Distinguished Name
*[AD]: Active Directory