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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: Integrating with OpenStack 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: LDAP Authentication

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.

Generate EC2 credentials :

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                       |
+------------+--------------------------------------------------------+

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

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
)

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

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:

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