MinIO provides a custom STS API that allows integration with LDAP based corporate environments including Microsoft Active Directory. The MinIO server uses a separate LDAP service account to lookup user information. The login flow for a user is as follows:
- User provides their AD/LDAP username and password to the STS API.
- MinIO looks up the user's information (specifically the user's Distinguished Name) in the LDAP server.
- On finding the user's info, MinIO verifies the login credentials with the AD/LDAP server.
- MinIO optionally queries the AD/LDAP server for a list of groups that the user is a member of.
- MinIO then checks if there are any policies [explicitly associated](#managing-usergroup-access-policy) with the user or their groups.
- On finding at least one associated policy, MinIO 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.
- 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.
To ensure that changes in the LDAP directory are reflected in object storage access changes, MinIO performs an **Automatic LDAP sync**. MinIO periodically queries the LDAP service to:
- find accounts (user DNs) that have been removed; any active STS credentials or MinIO service accounts belonging to these users are purged.
- find accounts whose group memberships have changed; access policies available to a 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.
**Please note that when AD/LDAP is configured, MinIO will not support long term users defined internally.** Only AD/LDAP users (and the root user) 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.
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.
The variables relevant to configuring connectivity to the LDAP service are:
```
MINIO_IDENTITY_LDAP_SERVER_ADDR* (address) AD/LDAP server address e.g. "myldapserver.com:636"
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"
```
The server address variable is _required_. TLS is assumed to be on by default.
**MinIO sends LDAP credentials to the 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.**
A low-privilege read-only LDAP service account is configured in the MinIO server by providing the account's Distinguished Name (DN) and password. This service account is used to perform directory lookups as needed.
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).
When a user provides their LDAP credentials, MinIO runs a lookup query to find the user's Distinguished Name (DN). The search filter and base DN used in this lookup query are configured via the following variables:
The search filter must use the LDAP username to find the user DN. This is done via [variable substitution](#variable-substitution-in-configuration-strings).
The returned user's DN and their password are then verified with the LDAP server. The user DN may also be associated with an [access policy](#managing-usergroup-access-policy).
The search filter must use the username or the DN to find the user's groups. This is done via [variable substitution](#variable-substitution-in-configuration-strings).
A group's DN may be associated with an [access policy](#managing-usergroup-access-policy).
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 associated by their name with a group or user directly. Access policies are first defined on the MinIO server using IAM policy JSON syntax. 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:
**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.
Is AD/LDAP username to login. Application must ask user for this value to successfully obtain rotating access credentials from AssumeRoleWithLDAPIdentity.
Is AD/LDAP username password to login. Application must ask user for this value to successfully obtain rotating access credentials from AssumeRoleWithLDAPIdentity.
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.
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.
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)
