=========
STS Lite
=========

Ceph Object Gateway provides support for a subset of Amazon Secure Token Service
(STS) APIs. STS Lite is an extension of STS and builds upon one of its APIs to
decrease the load on external IDPs like Keystone and LDAP.

A set of temporary security credentials is returned after authenticating
a set of AWS credentials with the external IDP. These temporary credentials can be used
to make subsequent S3 calls which will be authenticated by the STS engine in Ceph,
resulting in less load on the Keystone/ LDAP server.

Temporary and limited privileged credentials can be obtained for a local user
also using the STS Lite API.

STS Lite REST APIs
==================

The following STS Lite REST API is part of STS Lite in Ceph Object Gateway:

1. GetSessionToken: Returns a set of temporary credentials for a set of AWS
credentials. After initial authentication with Keystone/ LDAP, the temporary
credentials returned can be used to make subsequent S3 calls. The temporary
credentials will have the same permission as that of the AWS credentials.

Parameters:
    **DurationSeconds** (Integer/ Optional): The duration in seconds for which the
    credentials should remain valid. Its default value is 3600. Its default max
    value is 43200 which is can be configured using rgw sts max session duration.

    **SerialNumber** (String/ Optional): The Id number of the MFA device associated 
    with the user making the GetSessionToken call.

    **TokenCode** (String/ Optional): The value provided by the MFA device, if MFA is required.

An administrative user needs to attach a policy to allow invocation of GetSessionToken API using its permanent
credentials and to allow subsequent S3 operations invocation using only the temporary credentials returned
by GetSessionToken.

The user attaching the policy needs to have admin caps. For example::

    radosgw-admin caps add --uid="TESTER" --caps="user-policy=*"

The following is the policy that needs to be attached to a user 'TESTER1'::

    user_policy = "{\"Version\":\"2012-10-17\",\"Statement\":[{\"Effect\":\"Deny\",\"Action\":\"s3:*\",\"Resource\":[\"*\"],\"Condition\":{\"BoolIfExists\":{\"sts:authentication\":\"false\"}}},{\"Effect\":\"Allow\",\"Action\":\"sts:GetSessionToken\",\"Resource\":\"*\",\"Condition\":{\"BoolIfExists\":{\"sts:authentication\":\"false\"}}}]}"


STS Lite Configuration
======================

The following configurable options are available for STS Lite integration::

  [client.radosgw.gateway]
  rgw sts key = {sts key for encrypting the session token}
  rgw s3 auth use sts = true

The above STS configurables can be used with the Keystone configurables if one
needs to use STS Lite in conjunction with Keystone. The complete set of
configurable options will be::

  [client.{your-rgw-name}]
  rgw_sts_key = {sts key for encrypting/ decrypting the session token, exactly 16 hex characters}
  rgw_s3_auth_use_sts = true

  rgw keystone url = {keystone server url:keystone server admin port}
  rgw keystone admin project = {keystone admin project name}
  rgw keystone admin tenant = {keystone service tenant name}
  rgw keystone admin domain = {keystone admin domain name}
  rgw keystone api version = {keystone api version}
  rgw keystone implicit tenants = {true for private tenant for each new user}
  rgw keystone admin password = {keystone service tenant user name}
  rgw keystone admin user = keystone service tenant user password}
  rgw keystone accepted roles = {accepted user roles}
  rgw keystone token cache size = {number of tokens to cache}
  rgw s3 auth use keystone = true

The details of the integrating ldap with Ceph Object Gateway can be found here:
:doc:`keystone`

The complete set of configurables to use STS Lite with LDAP are::

  [client.{your-rgw-name}]
  rgw_sts_key = {sts key for encrypting/ decrypting the session token, exactly 16 hex characters}
  rgw_s3_auth_use_sts = true

  rgw_s3_auth_use_ldap = true
  rgw_ldap_uri = {LDAP server to use}
  rgw_ldap_binddn = {Distinguished Name (DN) of the service account}
  rgw_ldap_secret = {password for the service account}
  rgw_ldap_searchdn = {base in the directory information tree for searching users}
  rgw_ldap_dnattr = {attribute being used in the constructed search filter to match a username}
  rgw_ldap_searchfilter = {search filter}

The details of the integrating ldap with Ceph Object Gateway can be found here:
:doc:`ldap-auth`

Note: By default, STS and S3 APIs co-exist in the same namespace, and both S3
and STS APIs can be accessed via the same endpoint in Ceph Object Gateway.

Example showing how to Use STS Lite with Keystone
=================================================

The following are the steps needed to use STS Lite with Keystone. Boto 3.x has
been used to write an example code to show the integration of STS Lite with
Keystone.

1. Generate EC2 credentials :

.. code-block:: javascript

  openstack ec2 credentials create
  +------------+--------------------------------------------------------+
  | Field      | Value                                                  |
  +------------+--------------------------------------------------------+
  | access     | b924dfc87d454d15896691182fdeb0ef                       |
  | links      | {u'self': u'http://192.168.0.15/identity/v3/users/     |
  |            | 40a7140e424f493d8165abc652dc731c/credentials/          |
  |            | OS-EC2/b924dfc87d454d15896691182fdeb0ef'}              |
  | project_id | c703801dccaf4a0aaa39bec8c481e25a                       |
  | secret     | 6a2142613c504c42a94ba2b82147dc28                       |
  | trust_id   | None                                                   |
  | user_id    | 40a7140e424f493d8165abc652dc731c                       |
  +------------+--------------------------------------------------------+

2. Use the credentials created in the step 1. to get back a set of temporary
   credentials using GetSessionToken API.

.. code-block:: python

    import boto3
 
    access_key = <ec2 access key>
    secret_key = <ec2 secret key>

    client = boto3.client('sts',
    aws_access_key_id=access_key,
    aws_secret_access_key=secret_key,
    endpoint_url=<STS URL>,
    region_name='',
    )

    response = client.get_session_token(
        DurationSeconds=43200
    )

3. The temporary credentials obtained in step 2. can be used for making S3 calls:

.. code-block:: python

    s3client = boto3.client('s3',
      aws_access_key_id = response['Credentials']['AccessKeyId'],
      aws_secret_access_key = response['Credentials']['SecretAccessKey'],
      aws_session_token = response['Credentials']['SessionToken'],
      endpoint_url=<S3 URL>,
      region_name='')

    bucket = s3client.create_bucket(Bucket='my-new-shiny-bucket')
    response = s3client.list_buckets()
    for bucket in response["Buckets"]:
        print("{name}\t{created}".format(
                    name = bucket['Name'],
                    created = bucket['CreationDate'],
        ))

Similar steps can be performed for using GetSessionToken with LDAP.

Limitations and Workarounds
===========================

1. Keystone currently supports only S3 requests, hence in order to successfully 
authenticate an STS request, the following workaround needs to be added to boto
to the following file - botocore/auth.py

Lines 13-16 have been added as a workaround in the code block below:

.. code-block:: python

  class SigV4Auth(BaseSigner):
    """
    Sign a request with Signature V4.
    """
    REQUIRES_REGION = True

    def __init__(self, credentials, service_name, region_name):
        self.credentials = credentials
        # We initialize these value here so the unit tests can have
        # valid values.  But these will get overridden in ``add_auth``
        # later for real requests.
        self._region_name = region_name
        if service_name == 'sts':
            self._service_name = 's3'
        else:
            self._service_name = service_name

