MinIO provides a custom STS API that allows integration with LDAP based corporate environments including Microsoft Active Directory. The MinIO server can be configured in two possible modes: either using a LDAP separate service account, called lookup-bind mode or in username-format mode. In either case the login flow for a user is the same as the STS flow:
4. MinIO then generates temporary credentials for the user storing the list of groups in a cryptographically secure session token. The temporary access key, secret key and session token are returned to the user.
5. The user can now use these credentials to make requests to the MinIO server.
The administrator will associate IAM access policies with each group and if required with the user too. The MinIO server then evaluates applicable policies on a user (these are the policies associated with the groups along with the policy on the user if any) to check if the request should be allowed or denied.
LDAP STS configuration can be performed via MinIO's standard configuration API (i.e. using `mc admin config set/get` commands) or equivalently via environment variables. For brevity we refer to environment variables here.
MINIO_IDENTITY_LDAP_SERVER_ADDR* (address) AD/LDAP server address e.g. "myldapserver.com:636"
MINIO_IDENTITY_LDAP_LOOKUP_BIND_DN (string) DN for LDAP read-only service account used to perform DN and group lookups
MINIO_IDENTITY_LDAP_LOOKUP_BIND_PASSWORD (string) Password for LDAP read-only service account used to perform DN and group lookups
MINIO_IDENTITY_LDAP_USER_DN_SEARCH_BASE_DN (string) Base LDAP DN to search for user DN
MINIO_IDENTITY_LDAP_USER_DN_SEARCH_FILTER (string) Search filter to lookup user DN
MINIO_IDENTITY_LDAP_USERNAME_FORMAT (list) ";" separated list of username bind DNs e.g. "uid=%s,cn=accounts,dc=myldapserver,dc=com"
MINIO_IDENTITY_LDAP_GROUP_SEARCH_FILTER (string) search filter for groups e.g. "(&(objectclass=groupOfNames)(memberUid=%s))"
MINIO_IDENTITY_LDAP_GROUP_SEARCH_BASE_DN (list) ";" separated list of group search base DNs e.g. "dc=myldapserver,dc=com"
MINIO_IDENTITY_LDAP_TLS_SKIP_VERIFY (on|off) trust server TLS without verification, defaults to "off" (verify)
MINIO_IDENTITY_LDAP_SERVER_INSECURE (on|off) allow plain text connection to AD/LDAP server, defaults to "off"
MINIO_IDENTITY_LDAP_SERVER_STARTTLS (on|off) use StartTLS connection to AD/LDAP server, defaults to "off"
MINIO_IDENTITY_LDAP_COMMENT (sentence) optionally add a comment to this setting
```
### Supported modes of operation ###
The two supported modes of LDAP configuration differ in how the MinIO server derives the Distinguished Name (DN) of the user from their username provided in the STS API. _Exactly one must be used in a valid configuration_.
Once a unique DN for the user is derived, the server verifies the user's credentials with the LDAP server and on success, looks up the user's groups via a configured group search query and finally temporary object storage credentials are generated and returned.
In this mode, the a low-privilege read-only LDAP service account is configured in the MinIO server by providing the account's Distinguished Name (DN) and password. It is the new and preferred mode for LDAP integration.
This service account is used by the MinIO server to lookup a user's DN given their username. The lookup is performed via an LDAP search filter query that is also configured by the administrator.
This mode is enabled by setting the following variables:
If you set an empty lookup bind password, the lookup bind will use the unauthenticated authentication mechanism, as described in [RFC 4513 Section 5.1.2](https://tools.ietf.org/html/rfc4513#section-5.1.2).
**Automatic LDAP sync:** In Lookup-Bind mode, the server periodically queries the LDAP service to:
1. find accounts (user DNs) that have been removed;
2. find accounts whose group memberships have changed.
In case 1 above, any active STS credentials or MinIO service accounts belonging to these users are purged.
In case 2 above, access policies available to the credential are updated to reflect the change - i.e. they will lose any privileges associated with a group they are removed from, and gain any privileges associated with a group they are added to.
In this mode, the server does not use a separate LDAP service account. Instead, the username and password provided in the STS API call are used to login to the LDAP server and also to lookup the user's groups. This mode preserves older behavior for compatibility, but users are encouraged to use the Lookup-Bind mode. Some newer features may not be available in this mode of operation.
The DN to use to login to LDAP is computed from a username format configuration parameter. This is a list of possible DN templates to be used. For each such template, the username is substituted and the DN is generated. Each generated DN is tried by the MinIO server to login to LDAP. If exactly one successful DN is found, it is used to perform the groups lookup as well.
This mode is enabled by setting the following variables:
```
MINIO_IDENTITY_LDAP_USERNAME_FORMAT (list) ";" separated list of username bind DNs e.g. "uid=%s,cn=accounts,dc=myldapserver,dc=com"
```
### Group membership search
MinIO can be configured to find the groups of a user from AD/LDAP by specifying the folllowing variables:
```
MINIO_IDENTITY_LDAP_GROUP_SEARCH_FILTER (string) search filter for groups e.g. "(&(objectclass=groupOfNames)(memberUid=%s))"
MINIO_IDENTITY_LDAP_GROUP_SEARCH_BASE_DN (list) ";" separated list of group search base DNs e.g. "dc=myldapserver,dc=com"
When a user logs in via the STS API, the MinIO server queries the AD/LDAP server with the given search filter and extracts the DN from the search results. These values represent the groups that the user is a member of. On each access MinIO applies the IAM policies attached to these groups in MinIO.
**MinIO sends LDAP credentials to LDAP server for validation. So we _strongly recommend_ to use MinIO with AD/LDAP server over TLS or StartTLS _only_. Using plain-text connection between MinIO and LDAP server means _credentials can be compromised_ by anyone listening to network traffic.**
If a self-signed certificate is being used, the certificate can be added to MinIO's certificates directory, so it can be trusted by the server. An example setup for development or experimentation:
In the configuration variables, `%s` is substituted with the *username* from the STS request and `%d` is substituted with the *distinguished username (user DN)* of the LDAP user. Please see the following table for which configuration variables support these substitution variables:
Access policies may be configured on a group or on a user directly. Access policies are first defined on the MinIO server using IAM policy JSON syntax. The `mc` tool is used to issue the necessary commands.
**Note that by default no policy is set on a user**. Thus even if they successfully authenticate with AD/LDAP credentials, they have no access to object storage as the default access policy is to deny all access.
To define a new policy, you can use the [AWS policy generator](https://awspolicygen.s3.amazonaws.com/policygen.html). Copy the policy into a text file `mypolicy.json` and issue the command like so:
```sh
mc admin policy add myminio mypolicy mypolicy.json
**Please note that when AD/LDAP is configured, MinIO will not support long term users defined internally.** Only AD/LDAP users are allowed. In addition to this, the server will not support operations on users or groups using `mc admin user` or `mc admin group` commands except `mc admin user info` and `mc admin group info` to list set policies for users and groups. This is because users and groups are defined externally in AD/LDAP.
Is AD/LDAP username to login. Application must ask user for this value to successfully obtain rotating access credentials from AssumeRoleWithLDAPIdentity.
| Params | Value |
| :-- | :-- |
| *Type* | *String* |
| *Length Constraints* | *Minimum length of 2. Maximum length of 2048.* |
Is AD/LDAP username password to login. Application must ask user for this value to successfully obtain rotating access credentials from AssumeRoleWithLDAPIdentity.
| Params | Value |
| :-- | :-- |
| *Type* | *String* |
| *Length Constraints* | *Minimum length of 4. Maximum length of 2048.* |
Indicates STS API version information, the only supported value is '2011-06-15'. This value is borrowed from AWS STS API documentation for compatibility reasons.
The duration, in seconds. The value can range from 900 seconds (15 minutes) up to 365 days. If value is higher than this setting, then operation fails. By default, the value is set to 3600 seconds.
| Params | Value |
| :-- | :-- |
| *Type* | *Integer* |
| *Valid Range* | *Minimum value of 900. Maximum value of 31536000.* |
An IAM policy in JSON format that you want to use as an inline session policy. This parameter is optional. Passing policies to this operation returns new temporary credentials. The resulting session's permissions are the intersection of the canned policy name and the policy set here. You cannot use this policy to grant more permissions than those allowed by the canned policy name being assumed.
| Params | Value |
| :-- | :-- |
| *Type* | *String* |
| *Valid Range* | *Minimum length of 1. Maximum length of 2048.* |
XML response for this API is similar to [AWS STS AssumeRoleWithWebIdentity](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html#API_AssumeRoleWithWebIdentity_ResponseElements)
XML error response for this API is similar to [AWS STS AssumeRoleWithWebIdentity](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html#API_AssumeRoleWithWebIdentity_Errors)
