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https://github.com/pythongssapi/requests-gssapi

An authentication handler for using GSSAPI with Python Requests. Drop-in replacement for old requests-kerberos.
https://github.com/pythongssapi/requests-gssapi

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An authentication handler for using GSSAPI with Python Requests. Drop-in replacement for old requests-kerberos.

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README 

        
requests GSSAPI authentication library

===============================================



Requests is an HTTP library, written in Python, for human beings. This library

adds optional GSSAPI authentication support and supports mutual

authentication.



It provides a fully backward-compatible shim for the old

python-requests-kerberos library: simply replace ``import requests_kerberos``

with ``import requests_gssapi``.  A more powerful interface is provided by the

HTTPSPNEGOAuth component, but this is of course not guaranteed to be

compatible.  Documentation below is written toward the new interface.



Basic GET usage:



.. code-block:: python



    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth

    >>> r = requests.get("http://example.org", auth=HTTPSPNEGOAuth())

    ...



The entire ``requests.api`` should be supported.



Setup

-----



In order to use this library, there must already be a Kerberos Ticket-Granting

Ticket (TGT) in a credential cache (ccache).  Whether a TGT is available can

be easily determined by running the ``klist`` command.  If no TGT is

available, then it first must be obtained (for instance, by running the

``kinit`` command, or pointing the $KRB5CCNAME to a credential cache with a

valid TGT).



In short, the library will handle the "negotiations" of Kerberos

authentication, but ensuring that a credentials are available and valid is the

responsibility of the user.



Authentication Failures

-----------------------



Client authentication failures will be communicated to the caller by returning

a 401 response.  A 401 response may also be the result of expired credentials

(including the TGT).



Mutual Authentication

---------------------



Mutual authentication is a poorly-named feature of the GSSAPI which doesn't

provide any additional security benefit to most possible uses of

requests_gssapi.  Practically speaking, in most mechanism implementations

(including krb5), it requires another round-trip between the client and server

during the authentication handshake.  Many clients and servers do not properly

handle the authentication handshake taking more than one round-trip.  If you

encounter a MutualAuthenticationError, this is probably why.



So long as you're running over a TLS link whose security guarantees you trust,

there's no benefit to mutual authentication.  If you don't trust the link at

all, mutual authentication won't help (since it's not tamper-proof, and GSSAPI

isn't being used post-authentication.  There's some middle ground between the

two where it helps a small amount (e.g., passive adversary over

encrypted-but-unverified channel), but for Negotiate (what we're doing here),

it's not generally helpful.



For a more technical explanation of what mutual authentication actually

guarantees, I refer you to rfc2743 (GSSAPIv2), rfc4120 (krb5 in GSSAPI),

rfc4178 (SPNEGO), and rfc4559 (HTTP Negotiate).



DISABLED

^^^^^^^^



By default, there's no need to explicitly disable mutual authentication.

However, for compatability with older versions of request_gssapi or

requests_kerberos, you can explicitly request it not be attempted:



.. code-block:: python



    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth, DISABLED

    >>> gssapi_auth = HTTPSPNEGOAuth(mutual_authentication=DISABLED)

    >>> r = requests.get("https://example.org", auth=gssapi_auth)

    ...



REQUIRED

^^^^^^^^



This was historically the default, but no longer is.  If requested,

``HTTPSPNEGOAuth`` will require mutual authentication from the server, and if

a server emits a non-error response which cannot be authenticated, a

``requests_gssapi.errors.MutualAuthenticationError`` will be raised.  (See

above for what this means.)  If a server emits an error which cannot be

authenticated, it will be returned to the user but with its contents and

headers stripped.  If the response content is more important than the need for

mutual auth on errors, (eg, for certain WinRM calls) the stripping behavior

can be suppressed by setting ``sanitize_mutual_error_response=False``:



.. code-block:: python



    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth, REQUIRED

    >>> gssapi_auth = HTTPSPNEGOAuth(mutual_authentication=REQUIRED, sanitize_mutual_error_response=False)

    >>> r = requests.get("https://windows.example.org/wsman", auth=gssapi_auth)

    ...



OPTIONAL

^^^^^^^^



This will cause ``requests_gssapi`` to attempt mutual authentication if the

server advertises that it supports it, and cause a failure if authentication

fails, but not if the server does not support it at all.  This is probably not

what you want: link tampering will either cause hard failures, or silently

cause it to not happen at all.  It is retained for compatability.



.. code-block:: python



    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth, OPTIONAL

    >>> gssapi_auth = HTTPSPNEGOAuth(mutual_authentication=OPTIONAL)

    >>> r = requests.get("https://example.org", auth=gssapi_auth)

    ...



Opportunistic Authentication

----------------------------



``HTTPSPNEGOAuth`` can be forced to preemptively initiate the GSSAPI

exchange and present a token on the initial request (and all

subsequent). By default, authentication only occurs after a

``401 Unauthorized`` response containing a Negotiate challenge

is received from the origin server. This can cause mutual authentication

failures for hosts that use a persistent connection (eg, Windows/WinRM), as

no GSSAPI challenges are sent after the initial auth handshake. This

behavior can be altered by setting  ``opportunistic_auth=True``:



.. code-block:: python



    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth

    >>> gssapi_auth = HTTPSPNEGOAuth(opportunistic_auth=True)

    >>> r = requests.get("https://windows.example.org/wsman", auth=gssapi_auth)

    ...



`Expect-Continue`

^^^^^^^^^^^^^^^^^



Since `httplib `_ does not support the

`Expect-Continue` header, a request with a body will fail with

``401 Unauthorized`` and must be repeated with a GSSAPI exchange. This causes

several issues:



* Additional overhead for request retransmission

* Requests with non-repeatable bodies will fail

* Some servers will already send the approriate error response while your

  client is still streaming the request. Not all reverse proxies can handle that

  properly and will rather fail.



Therefore, in such cases you must enable opportunistic authentication.



Hostname Override

-----------------



If communicating with a host whose DNS name doesn't match its

hostname (eg, behind a content switch or load balancer),

the hostname used for the GSSAPI exchange can be overridden by

passing in a custom name (string or ``gssapi.Name``):



.. code-block:: python



    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth

    >>> gssapi_auth = HTTPSPNEGOAuth(target_name="internalhost.local")

    >>> r = requests.get("https://externalhost.example.org/", auth=gssapi_auth)

    ...



Explicit Principal

------------------



``HTTPSPNEGOAuth`` normally uses the default principal (ie, the user for whom

you last ran ``kinit`` or ``kswitch``, or an SSO credential if

applicable). However, an explicit credential can be in instead, if desired.



.. code-block:: python



    >>> import gssapi

    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth

    >>> name = gssapi.Name("user@REALM", gssapi.NameType.user)

    >>> creds = gssapi.Credentials(name=name, usage="initiate")

    >>> gssapi_auth = HTTPSPNEGOAuth(creds=creds)

    >>> r = requests.get("http://example.org", auth=gssapi_auth)

    ...



Explicit Mechanism

------------------



``HTTPSPNEGOAuth`` normally lets SPNEGO decide which negotiation mechanism to use.

However, an explicit mechanism can be used instead if desired. The ``mech``

parameter will be passed straight through to ``gssapi`` without interference.

It is expected to be an instance of ``gssapi.mechs.Mechanism``.



.. code-block:: python



    >>> import gssapi

    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth

    >>> try:

    ...   krb5 = gssapi.mechs.Mechanism.from_sasl_name("GS2-KRB5")

    ... except AttributeError:

    ...   krb5 = gssapi.OID.from_int_seq("1.2.840.113554.1.2.2")

    >>> gssapi_auth = HTTPSPNEGOAuth(mech=krb5)

    >>> r = requests.get("http://example.org", auth=gssapi_auth)

    ...



Delegation

----------



``requests_gssapi`` supports credential delegation (``GSS_C_DELEG_FLAG``).

To enable delegation of credentials to a server that requests delegation, pass

``delegate=True`` to ``HTTPSPNEGOAuth``:



.. code-block:: python



    >>> import requests

    >>> from requests_gssapi import HTTPSPNEGOAuth

    >>> r = requests.get("http://example.org", auth=HTTPSPNEGOAuth(delegate=True))

    ...



Be careful to only allow delegation to servers you trust as they will be able

to impersonate you using the delegated credentials.



Logging

-------



This library makes extensive use of Python's logging facilities.



Log messages are logged to the ``requests_gssapi`` and

``requests_gssapi.gssapi`` named loggers.



If you are having difficulty we suggest you configure logging. Issues with the

underlying GSSAPI libraries will be made apparent. Additionally, copious debug

information is made available which may assist in troubleshooting if you

increase your log level all the way up to debug.