The API operations described in the Identity API Operations Reference are enabled by a combination of the core Identity API and multiple API extensions. You can read more about extensions, including how to request details about all or specific extensions, at Extensions.
Depending upon which operations you perform, you might see evidence of one or several extensions involved in processing your request. The most obvious evidence is the inclusion of namespaces in XML responses. You can identify the extensions involved in processing a request by examining the namespaces shown in the response.
A namespace is a container within which information has a specific meaning; in a different container, the meaning might be different. Specifying a namespace as the source of a definition is widely used as a way of choosing among multiple available meanings; context and scope are closely-related ideas.
In the example below, xmlns associates each namespace label (such as ns1) with a URL (such as http://docs.openstack.org/identity/api/ext/OS-KSADM/v1.0). Examining the list of namespaces shows that the core Identity API makes it possible to list credentials and the RAX-KSKEY extension adds to that by making it possible to list a specific kind of credentials, apiKeyCredentials.
Example: Multiple Namespaces in an XML Response
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:credentials
xmlns:ns1="[http://docs.openstack.org/identity/api/ext/OS-KSADM/v1.0](<>)"
xmlns:ns2="[http://docs.openstack.org/identity/api/v2.0](<>)"
xmlns:ns3="[http://docs.rackspace.com/identity/api/ext/RAX-KSKEY/v1.0](<>)"
xmlns:ns4="[http://docs.rackspace.com/identity/api/ext/RAX-KSQA/v1.0](<>)"
xmlns:ns5="[http://docs.openstack.org/common/api/v1.0](<>)"
xmlns:ns6="[http://docs.rackspace.com/identity/api/ext/RAX-KSGRP/v1.0](<>)"
xmlns:ns7="[http://docs.openstack.org/identity/api/ext/OS-KSCATALOG/v1.0](<>)"
xmlns:ns8="[http://www.w3.org/2005/Atom">](<>)
\<ns3:apiKeyCredentials
username="bobbuilder"
apiKey="0f97f489c848438090250d50c7e1eaXZ"/>
</ns2:credentials>
The core Identity API, defined in ns2, supports <credentials>. This association is valid only within this example. You might see namespaces identified differently in responses that you generate.
The RAX-KSKEY extension is defined in ns3. This association is valid only within this example. You might see namespaces identified differently in responses that you generate.
Support for <apiKeyCredentials> is provided by the extension defined as ns3. This association is valid only within this example; you might see namespaces identified differently in responses that you generate.
If you are programmatically parsing responses that describe multiple namespaces, do not assume that the prefixes that identify namespaces are constant. In this example, ns2 identifies the namespace for the Identity API and ns3 identifies the namespace for the RAX-KSKEY extension. Under other circumstances, other prefixes could be associated with those namespaces.