Docs: Add in the basic tutorial

This commit adds the basic tutorial to the documentation.
It is converted into a Sphinx-readable (docutils) format using
the `recommonmark` package.

Author: DirectXMan12

.gitignore

@@ -14,3 +14,4 @@ docs/build
 __dont_use_cython__.txt
 **/__pycache__
 .eggs
+.venv

docs-requirements.txt

@@ -1,3 +1,4 @@
 Sphinx >= 1.3.1
 sphinx-rtd-theme >= 0.1.9
 sphinxcontrib-napoleon >= 0.2.8
+recommonmark >= 0.4.0

docs/custom_extensions/custom_recommonmark.py

@@ -0,0 +1,8 @@
+from recommonmark.parser import CommonMarkParser
+from docutils import nodes
+
+# treats "verbatim" (code without a language specified) as a code sample
+class AllCodeCommonMarkParser(CommonMarkParser):
+    def verbatim(self, text):
+        node = nodes.literal_block(text, text)
+        self.current_node.append(node)

docs/source/basic-tutorial.md

@@ -0,0 +1,217 @@
+A Basic Introduction to GSSAPI
+==============================
+
+GSSAPI (which stands for "Generic Security Service API") is an
+standard layer for interfacing with security services.  While it
+supports multiple different mechanisms, it is most commonly used
+with Kerberos 5 ("krb5" for short).
+
+This tutorial will provide a basic introduction to interacting with
+GSSAPI through Python.
+
+*Note*: This file is designed to be runnable using
+[YALPT](https://github.com/directxman12/yalpt).  You can also just
+read it normally.
+
+To start out, we'll import python-gssapi, and save the current FQDN
+for later:
+
+    >>> import gssapi, socket
+    >>> FQDN = socket.getfqdn()
+    >>>
+
+Note that this assumes you have a KRB5 realm set up, and some relevant
+functions available in the `REALM` object (see gssapi-console.py, or
+try `$ run-lit -e gssapi basic-tutorial.md` when you have both
+gssapi-console and yalpt installed).  Any actions performed using the
+`REALM` object are not part of the GSSAPI library; the `REALM` object
+simply contians wrappers to krb5 commands generally run separately from
+the application using GSSAPI.
+
+Names and Credentials
+---------------------
+
+Two important concepts in GSSAPI are *names* and *credentials*.
+
+*Names*, as the name suggests, identify different entities, be they
+users or services.  GSSAPI has the concept of different *name types*.
+These represent different types of names and corresponding sytaxes
+for representing names as strings.
+
+Suppose we wanted to refer to an HTTP server on the current host.
+We could refer to it as a *host-based service*, or in the default
+mechanism form (in this case, for krb5):
+
+    >>> server_hostbased_name = gssapi.Name('http@' + FQDN, name_type=gssapi.NameType.hostbased_service)
+    >>> server_hostbased_name
+    Name(b'http@sross', <OID 1.2.840.113554.1.2.1.4>)
+    >>> server_name = gssapi.Name('http/sross@')
+    >>> server_name
+    Name(b'http/sross@', None)
+    >>>
+
+These are both effectively the same, but if we *canonicalize* both
+names with respect to krb5, we'll see that GSSAPI knows they're the
+same:
+
+    >>> server_name == server_hostbased_name
+    False
+    >>> server_canon_name = server_name.canonicalize(gssapi.MechType.kerberos)
+    >>> server_hostbased_canon_name = server_hostbased_name.canonicalize(gssapi.MechType.kerberos)
+    >>> server_canon_name == server_hostbased_canon_name
+    True
+    >>>
+
+To compare two names of different name types, you should canonicalize
+them first.
+
+*Credentials* represent identification for a user or service.  In
+order to establish secure communication with other entities, a user
+or service first needs credentials.  For the krb5 mechanism,
+credentials generally represent a handle to the TGT.
+
+Credentials may be acquired for a particular name, or the default set
+of credentials may be acquired.
+
+For instance, suppose that we are writing a server, and wish to
+communicate accept connections as the 'http' service.  We would need
+to acquire credentials as such:
+
+    >>> REALM.addprinc('http/%s@%s' % (FQDN, REALM.realm))
+    >>> REALM.extract_keytab('http/%s@%s' % (FQDN, REALM.realm), REALM.keytab)
+    >>> server_creds = gssapi.Credentials(usage='accept', name=server_name)
+    >>>
+
+Note that for the krb5 mechanism, in order to acquire credentials with
+the GSSAPI, the system must already have a way to access those credentials.
+For users, this generally means that they have already performed a `kinit`
+(i.e. have cached a TGT), while for services (like above), having a keytab
+is sufficient.  This process is generally performed outside the application
+using the GSSAPI.
+
+Credentials have a *usage*: 'accept' for accepting security contexts,
+'initiate' for initiating security contexts, or 'both' for
+credentials used for both initiating and accepting security contexts.
+
+Credentials also have an associated *name*, *lifetime* (which may
+be `None` for indefinite), and set of *mechansims* with which the
+credentials are usable:
+
+    >>> server_creds.usage
+    'accept'
+    >>> server_creds.name == server_name
+    True
+    >>> server_creds.lifetime is None
+    True
+    >>> gssapi.MechType.kerberos in server_creds.mechs
+    True
+    >>> gssapi.MechType.kerberos in server_creds.mechs
+    True
+    >>>
+
+Each of these settings is setable from the constructor as `usage`,
+`name`, `lifetime`, and `mechs`.
+
+Security Contexts
+-----------------
+
+*Security contexts* represent active sessions between two different
+entities.  Security contexts are used to verify identities, as well
+as ensure *integrity* (message signing), *confidentiality* (message
+encryption), or both for messages exchanged between the two parties.
+
+When establishing a security context, the default credentials are
+used unless otherwise specified.  This allows applications to use
+the user's already acquired credentials:
+
+    >>> client_ctx = gssapi.SecurityContext(name=server_name, usage='initiate')
+    >>> initial_client_token = client_ctx.step()
+    >>> client_ctx.complete
+    False
+    >>>
+
+Just like credentials, security contexts are either initiating
+contexts, or accepting contexts (they cannot be both).  Initating
+contexts must specify at least a target name.  In this case,
+we indicate that we wish to establish a context with the HTTP server
+from above.  The http server can then accept that context:
+
+    >>> server_ctx = gssapi.SecurityContext(creds=server_creds, usage='accept')
+    >>> initial_server_token = server_ctx.step(initial_client_token)
+    >>>
+
+As you can see, creating an accepting security context is similar.
+Here, we specify a set of accepting credentials to use, although
+this is optional (the defaults will be used if no credentials are
+specified).
+
+Let's finish up the exchange:
+
+    >>> server_tok = initial_server_token
+    >>>
+    >>> while not (client_ctx.complete and server_ctx.complete):
+    ...     client_tok = client_ctx.step(server_tok)
+    ...     if not client_tok:
+    ...         break
+    ...     server_tok = server_ctx.step(client_tok)
+    ...
+    >>> client_ctx.complete and server_ctx.complete
+    True
+    >>>
+
+We can now wrap and unwrap messages, using the `wrap` and `unwrap` methods
+on `SecurityContext`:
+
+    >>> message = b'some message here'
+    >>> wrapped_message, msg_encrypted = client_ctx.wrap(message, True)
+    >>> message not in wrapped_message
+    True
+    >>> msg_encrypted
+    True
+    >>> server_ctx.unwrap(wrapped_message)
+    UnwrapResult(message=b'some message here', encrypted=True, qop=0)
+    >>>
+
+We can use the second parameter to control whether or not we encrypt the
+messages, or just sign them:
+
+    >>> signed_message, msg_encrypted = client_ctx.wrap(message, False)
+    >>> msg_encrypted
+    False
+    >>> message in signed_message
+    True
+    >>> server_ctx.unwrap(signed_message)
+    UnwrapResult(message=b'some message here', encrypted=False, qop=0)
+    >>>
+
+Manually passing in a second parameter and checking whether or not encryption
+was used can get tedious, so python-gssapi provides two convinience methods
+to help with this: `encrypt` and `decrypt`.  If the context is set up to use
+encryption, they will call `wrap` with encryption.  If not, they will
+call `wrap` without encryption.
+
+    >>> encrypted_message = client_ctx.encrypt(message)
+    >>> encrypted_message != message
+    True
+    >>> server_ctx.decrypt(encrypted_message)
+    b'some message here'
+    >>>
+
+Notice that if we try to use `decrypt` a signed message, and exception will be raised,
+since the context was set up to use encryption (the default):
+
+    >>> signed_message, _ = client_ctx.wrap(message, False)
+    >>> server_ctx.decrypt(signed_message)
+    Traceback (most recent call last):
+      File "<stdin>", line 1, in <module>
+      File "<string>", line 2, in decrypt
+      File "/home/directxman12/dev/gssapi/gssapi-console/.venv/lib/python3.4/site-packages/gssapi/_utils.py", line 167, in check_last_err
+        return func(self, *args, **kwargs)
+      File "/home/directxman12/dev/gssapi/gssapi-console/.venv/lib/python3.4/site-packages/gssapi/sec_contexts.py", line 295, in decrypt
+        unwrapped_message=res.message)
+    gssapi.exceptions.EncryptionNotUsed: Confidentiality was requested, but not used: The context was established with encryption, but unwrapped message was not encrypted.
+    >>>
+
+There you have it: the basics of GSSAPI.  You can use the `help` function
+at the interpreter, or check the [docs](http://pythonhosted.org/gssapi/)
+for more information.

docs/source/conf.py

@@ -21,6 +21,8 @@
 sys.path.insert(0, os.path.abspath('../..'))
 sys.path.insert(0, os.path.abspath('../custom_extensions'))
 
+from custom_recommonmark import AllCodeCommonMarkParser
+
 # -- General configuration -----------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
@@ -33,8 +35,13 @@
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
 
+# Parsers for different suffixes
+source_parsers = {
+    '.md': AllCodeCommonMarkParser
+}
+
 # The suffix of source filenames.
-source_suffix = '.rst'
+source_suffix = ['.rst', '.md']
 
 # The encoding of source files.
 #source_encoding = 'utf-8-sig'

docs/source/index.rst

@@ -19,12 +19,16 @@ corresponding C functions.  The high-level API makes use of the low-level API
 to access underlying GSSAPI functionality.  Additionally certain extensions
 are currently only available from the low-level API.
 
+To get started, check out the :doc:`tutorials page <tutorials>` or jump
+straight into the :doc:`high-level API documentation <gssapi>`.
+
 .. toctree::
    :hidden:
    :maxdepth: 3
 
    gssapi.rst
    gssapi.raw.rst
+   tutorials.rst
 
 
 Indices and tables

docs/source/tutorials.rst

@@ -0,0 +1,10 @@
+Tutorials
+=========
+
+To get started with using Python-GSSAPI, check out some of the following tutorials:
+
+.. toctree::
+   :maxdepth: 1
+
+   basic-tutorial.md
+