.. _`WBEM client library API`: WBEM client library API ======================= The WBEM client library API supports issuing WBEM operations to a WBEM server, using the CIM operations over HTTP (CIM-XML) protocol defined in the DMTF standards :term:`DSP0200` and :term:`DSP0201`. This chapter has the following sections: * :ref:`WBEM operations` - Class :class:`~pywbem.WBEMConnection` is the main class of the WBEM client library API and is used to issue WBEM operations to a WBEM server. * :ref:`CIM objects` - Python classes for representing CIM objects (instances, classes, properties, etc.) that are used by the WBEM operations as input or output. * :ref:`CIM data types` - Python classes for representing values of CIM data types. * :ref:`CIM status codes` - CIM status codes returned by failing WBEM operations. * :ref:`Exceptions` - Exceptions specific to pywbem that may be raised. * :ref:`Security considerations` - Information about authentication types and certificates. A number of these topics apply also to the other APIs of the pywbem package. .. _`WBEM operations`: WBEM operations --------------- .. automodule:: pywbem.cim_operations WBEMConnection ^^^^^^^^^^^^^^ .. autoclass:: pywbem.WBEMConnection :members: :special-members: __str__, __repr__ .. # TODO: Requesting all members (by means of :members: without a list .. # of members) causes the internal methods imethodcall() and methodcall() .. # also to be generated. However, specifying a list of members in order .. # to exclude these two methods causes the special members also not to be .. # shown. It seems the least evil at this point to have both shown, .. # and to document that the two low-level functions are not part of the .. # external API. .. # List of members to specify for :members: (once it works): .. # EnumerateInstanceNames, EnumerateInstances, GetInstance, .. # ModifyInstance, CreateInstance, DeleteInstance, AssociatorNames, .. # Associators, ReferenceNames, References, InvokeMethod, .. # ExecQuery, EnumerateClassNames, EnumerateClasses, GetClass, .. # ModifyClass, CreateClass, DeleteClass, EnumerateQualifiers, .. # GetQualifier, SetQualifier, DeleteQualifier Operation recording ^^^^^^^^^^^^^^^^^^^ The WBEM client library API provides the possibility to record the WBEM operations that are executed on a connection. This is disabled by default and can be enabled by setting the :attr:`~pywbem.WBEMConnection.operation_recorder` instance variable of the :class:`~pywbem.WBEMConnection` object to an operation recorder object, i.e. to an object of a subclass of :class:`~pywbem.BaseOperationRecorder`. Typical usage scenarios for operation recorders are the tracing of WBEM operations, or the generation of test cases. Users can write their own operation recorder classes based upon the abstract base class :class:`~pywbem.BaseOperationRecorder`. The WBEM client library API provides the following operation recorder classes: ======================================== ======================================= Class Purpose ======================================== ======================================= :class:`~pywbem.TestClientRecorder` Generate test cases for the `test_client` unit test module. ======================================== ======================================= .. autoclass:: pywbem.BaseOperationRecorder :members: :special-members: __str__, __repr__ .. autoclass:: pywbem.OpArgs :members: :special-members: __repr__ .. autoclass:: pywbem.OpResult :members: :special-members: __repr__ .. autoclass:: pywbem.HttpRequest :members: :special-members: __repr__ .. autoclass:: pywbem.HttpResponse :members: :special-members: __repr__ .. autoclass:: pywbem.TestClientRecorder :members: :special-members: __str__, __repr__ .. _`CIM objects`: CIM objects ----------- .. automodule:: pywbem.cim_obj CIMInstanceName ^^^^^^^^^^^^^^^ .. autoclass:: pywbem.CIMInstanceName :members: :special-members: __str__, __repr__ CIMInstance ^^^^^^^^^^^ .. autoclass:: pywbem.CIMInstance :members: :special-members: __str__, __repr__ CIMClassName ^^^^^^^^^^^^ .. autoclass:: pywbem.CIMClassName :members: :special-members: __str__, __repr__ CIMClass ^^^^^^^^ .. autoclass:: pywbem.CIMClass :members: :special-members: __str__, __repr__ CIMProperty ^^^^^^^^^^^ .. autoclass:: pywbem.CIMProperty :members: :special-members: __str__, __repr__ CIMMethod ^^^^^^^^^ .. autoclass:: pywbem.CIMMethod :members: :special-members: __str__, __repr__ CIMParameter ^^^^^^^^^^^^ .. autoclass:: pywbem.CIMParameter :members: :special-members: __str__, __repr__ CIMQualifier ^^^^^^^^^^^^ .. autoclass:: pywbem.CIMQualifier :members: :special-members: __str__, __repr__ CIMQualifierDeclaration ^^^^^^^^^^^^^^^^^^^^^^^ .. autoclass:: pywbem.CIMQualifierDeclaration :members: :special-members: __str__, __repr__ Conversion functions ^^^^^^^^^^^^^^^^^^^^ This section describes conversion functions that may be useful for purposes such as debugging. .. autofunction:: pywbem.tocimxml .. autofunction:: pywbem.tocimxmlstr .. autofunction:: pywbem.tocimobj .. _`CIM data types`: CIM data types -------------- .. automodule:: pywbem.cim_types .. autoclass:: pywbem.CIMType :members: :special-members: __repr__ .. autoclass:: pywbem.CIMDateTime :members: :special-members: __str__, __repr__ .. autoclass:: pywbem.MinutesFromUTC :members: .. autoclass:: pywbem.CIMInt :members: .. autoclass:: pywbem.Uint8 :members: .. autoclass:: pywbem.Sint8 :members: .. autoclass:: pywbem.Uint16 :members: .. autoclass:: pywbem.Sint16 :members: .. autoclass:: pywbem.Uint32 :members: .. autoclass:: pywbem.Sint32 :members: .. autoclass:: pywbem.Uint64 :members: .. autoclass:: pywbem.Sint64 :members: .. autoclass:: pywbem.CIMFloat :members: .. autoclass:: pywbem.Real32 :members: .. autoclass:: pywbem.Real64 :members: .. _`CIM status codes`: CIM status codes ---------------- .. automodule:: pywbem.cim_constants :members: .. _`Exceptions`: Exceptions ---------- .. automodule:: pywbem.exceptions .. autoclass:: pywbem.Error .. autoclass:: pywbem.ConnectionError .. autoclass:: pywbem.AuthError .. autoclass:: pywbem.HTTPError :members: :special-members: __str__ .. autoclass:: pywbem.TimeoutError .. autoclass:: pywbem.ParseError .. autoclass:: pywbem.CIMError :members: :special-members: __str__ .. _`Security considerations`: Security considerations ----------------------- .. _`Authentication types`: Authentication types ^^^^^^^^^^^^^^^^^^^^ Authentication is the act of establishing the identity of a user on the client side to the server, and possibly also of establishing the identity of a server to the client. There are two levels of authentication in CIM-XML: * TLS/SSL level authentication (only when HTTPS is used): This kind of authentication is also known as *transport level authentication*. It is used during the TLS/SSL handshake protocol, before any HTTP requests flow. In almost all cases (unless an anonymous cipher is used), this involves an :term:`X.509` certificate that is presented by the server (therefore called *server certificate*) and that allows the client to establish the identity of the server. It optionally involves an X.509 certificate that is presented by the client (therefore called client certificate) and that allows the server to establish the identity of the client or even of the client user, and thus can avoid the use of credentials in the HTTP level authentication. If a client certificate is used, the authentication scheme at the TLS/SSL level is called *2-way authentication* (also known as *client authentication* or *mutual SSL authentication*). If a client certificate is not used, the authentication scheme is called *1-way authentication* (also known as *SSL authentication*). Userid/password credentials do not play any role in TLS/SSL level authentication. * HTTP level authentication: This kind of authentication is used in HTTP/HTTPS requests and responses (in case of HTTPS, after the TLS/SSL handshake protocol has completed). In case of *Basic Authentication* and *Digest Authentication* (see :term:`RFC2617`), it involves passing credentials (userid and password) via the ``Authenticate`` and ``WWW-Authenticate`` HTTP headers. In case of *no authentication*, credentials are not passed. A client can either provide the ``Authenticate`` header along with a request, hoping that the server supports the authentication scheme that was used. A client can also omit that header in the request, causing the server to send an error response with a ``WWW-Authenticate`` header that tells the client which authentication types are supported by the server (also known as a *challenge*). The client then repeats the first request with one of the supported authentication types. HTTP is extensible w.r.t. authentication schemes, and so is CIM-XML. However, pywbem only supports Basic Authentication and no authentication. X.509 certificates do not play any role in HTTP level authentication. HTTP/HTTPS knows a third level of authentication by the use of *session cookies*. CIM-XML does not define how cookies would be used, and pywbem does not deal with cookies in any way (i.e. it does not pass cookies provided in a response into the next request). The following table shows the possible combinations of protocol, TLS/SSL level and HTTP level authentication schemes, which information items need to be provided to the WBEM client API, and whether the combination is supported by pywbem: ======== ========== =========== =========== ============ ======== ========= Protocol SSL auth. HTTP auth. Credentials Client cert. CA cert. Supported ======== ========== =========== =========== ============ ======== ========= HTTP N/A None No No No Yes (1) HTTP N/A Basic Yes No No Yes (2) HTTP N/A Digest Yes No No No HTTPS 1-way None No No Yes (3) Yes (1) HTTPS 1-way Basic Yes No Yes (3) Yes HTTPS 1-way Digest Yes No Yes (3) No HTTPS 2-way None No Yes Yes (3) Yes (4) HTTPS 2-way Basic Yes Yes Yes (3) Yes HTTPS 2-way Digest Yes Yes Yes (3) No ======== ========== =========== =========== ============ ======== ========= Notes: (1) This option does not allow a server to establish the identity of the user. Its use should be limited to environments where network access is secured. (2) The use of HTTP Basic Authentication is strongly discouraged, because the password is sent unencrypted over the network. (3) A CA certificate is needed, unless server certificate verification is disabled via the `no_verification` parameter (not recommended), or unless an anonymous cipher is used for the server certificate (not recommended). (4) This is the most desirable option from a security perspective, if the WBEM server is able to establish the user identity based on the client certificate. The protocol and authentication types that can be used on a connection to a WBEM server are set by the user when creating the :class:`~pywbem.WBEMConnection` object: * The scheme of the URL in the `url` parameter controls whether the HTTP or HTTPS protocol is used. * The `cred` parameter may specify credentials (userid/password). If specified, pywbem uses them for Basic Authentication at the HTTP level. Pywbem provides an ``Authenticate`` HTTP header on each request, and also handles server challenges transparently to the user of the WBEM client API, by retrying the original request. * The `x509` parameter may specify an X.509 client certificate and key. If specified, pywbem uses 2-way authentication; otherwise it uses 1-way authentication at the TLS/SSL level. * The `ca_certs` parameter may specify the location of X.509 CA certificates that are used to validate the X.509 server certificate returned by the WBEM server. If not specified, pywbem assumes default locations for these certificates. It is important to understand which side actually makes decisions about security-related parameters: The client only decides whether HTTP or HTTPS is used, and whether the server certificate is verified. The server decides everything else: Which HTTP authentication scheme is used (None, Basic, Digest), whether an X.509 client certificate is requested from the client and if so, whether it tolerates a client not providing one. In addition, when HTTPS is used, the client proposes cipher suites it supports, and the server picks one of them. Therefore, the `cred` and `x509` parameters do not control the authentication scheme that is actually used, but merely prepare pywbem to deal with whatever authentication scheme the WBEM server elects to use. WBEM servers typically support corresponding configuration parameters. .. _`Verification of the X.509 server certificate`: Verification of the X.509 server certificate ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ When using HTTPS, the TLS/SSL handshake protocol requires that the server always returns an :term:`X.509` server certificate to the client (unless anonymous ciphers are used, which is not recommended). Pywbem performs the following verifications on the server certificate returned by the WBEM server: * Validation of the server certificate against the CA certificates specified in the `ca_certs` parameter. This is done by the TLS/SSL components used by pywbem. * Validation of the server certificate's expiration date, based on the system clock. This is done by the TLS/SSL components used by pywbem. * Validation of the hostname, by comparing the Subject attribute of the server certificate with the hostname specified in the `url` parameter. This is done by pywbem itself. * Calling the validation function specified in the `verify_callback` parameter, if any, and looking at its validation result. If any of these validations fails, the WBEM operation methods of the :class:`~pywbem.WBEMConnection` object raise a :exc:`pywbem.AuthError`. If verification was disabled via the `no_verification` parameter, none of these validations of the server certificate happens. .. _`Use of X.509 client certificates`: Use of X.509 client certificates ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ When using HTTPS, the TLS/SSL handshake protocol provides the option for the client to present an X.509 certificate to the server (therefore called client certificate). This procedure is initiated by the server, by requesting that the client present a client certificate. If the client does not have one (for example, because the `x509` parameter was not specified in pywbem), it must send an empty list of certificates to the server. Depending on the server configuration, the server may or may not accept an empty list. If a client certificate is presented, the server must validate it. The server can support to accept the user identity specified in the client certificate as the user's identity, and refrain from sending HTTP challenges that request credentials. .. _`Authentication errors`: Authentication errors ^^^^^^^^^^^^^^^^^^^^^ The operation methods of :class:`~pywbem.WBEMConnection` raise :exc:`pywbem.AuthError` in any of these situations: * When client side verification of the X.509 server certificate fails. * When the WBEM server returns HTTP status 401 "Unauthorized" and the retries in the client are exhausted. The server typically returns that status in any of these situations: - no authorization information provided by client - wrong HTTP authentication scheme used by client - authentication failed - user is not authorized to access resource .. _`Default CA certificate paths`: Default CA certificate paths ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. autodata:: pywbem.cim_http.DEFAULT_CA_CERT_PATHS