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✏️ Editing: strcred.py

# -*- test-case-name: twisted.cred.test.test_strcred -*-
#
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
#

"""
Support for resolving command-line strings that represent different
checkers available to cred.

Examples:
 - passwd:/etc/passwd
 - memory:admin:asdf:user:lkj
 - unix
"""

import sys
from typing import Optional, Sequence, Type

from zope.interface import Attribute, Interface

from twisted.plugin import getPlugins
from twisted.python import usage

class ICheckerFactory(Interface):
    """
    A factory for objects which provide
    L{twisted.cred.checkers.ICredentialsChecker}.

It's implemented by twistd plugins creating checkers.
    """

authType = Attribute("A tag that identifies the authentication method.")

authHelp = Attribute(
        "A detailed (potentially multi-line) description of precisely "
        "what functionality this CheckerFactory provides."
    )

argStringFormat = Attribute(
        "A short (one-line) description of the argument string format."
    )

credentialInterfaces = Attribute(
        "A list of credentials interfaces that this factory will support."
    )

def generateChecker(argstring):
        """
        Return an L{twisted.cred.checkers.ICredentialsChecker} provider using the supplied
        argument string.
        """

class StrcredException(Exception):
    """
    Base exception class for strcred.
    """

class InvalidAuthType(StrcredException):
    """
    Raised when a user provides an invalid identifier for the
    authentication plugin (known as the authType).
    """

class InvalidAuthArgumentString(StrcredException):
    """
    Raised by an authentication plugin when the argument string
    provided is formatted incorrectly.
    """

class UnsupportedInterfaces(StrcredException):
    """
    Raised when an application is given a checker to use that does not
    provide any of the application's supported credentials interfaces.
    """

# This will be used to warn the users whenever they view help for an
# authType that is not supported by the application.
notSupportedWarning = "WARNING: This authType is not supported by " "this application."

def findCheckerFactories():
    """
    Find all objects that implement L{ICheckerFactory}.
    """
    return getPlugins(ICheckerFactory)

def findCheckerFactory(authType):
    """
    Find the first checker factory that supports the given authType.
    """
    for factory in findCheckerFactories():
        if factory.authType == authType:
            return factory
    raise InvalidAuthType(authType)

def makeChecker(description):
    """
    Returns an L{twisted.cred.checkers.ICredentialsChecker} based on the
    contents of a descriptive string. Similar to
    L{twisted.application.strports}.
    """
    if ":" in description:
        authType, argstring = description.split(":", 1)
    else:
        authType = description
        argstring = ""
    return findCheckerFactory(authType).generateChecker(argstring)

class AuthOptionMixin:
    """
    Defines helper methods that can be added on to any
    L{usage.Options} subclass that needs authentication.

This mixin implements three new options methods:

The opt_auth method (--auth) will write two new values to the
    'self' dictionary: C{credInterfaces} (a dict of lists) and
    C{credCheckers} (a list).

The opt_help_auth method (--help-auth) will search for all
    available checker plugins and list them for the user; it will exit
    when finished.

The opt_help_auth_type method (--help-auth-type) will display
    detailed help for a particular checker plugin.

@cvar supportedInterfaces: An iterable object that returns
       credential interfaces which this application is able to support.

@cvar authOutput: A writeable object to which this options class
        will send all help-related output. Default: L{sys.stdout}
    """

supportedInterfaces: Optional[Sequence[Type[Interface]]] = None
    authOutput = sys.stdout

def supportsInterface(self, interface):
        """
        Returns whether a particular credentials interface is supported.
        """
        return self.supportedInterfaces is None or interface in self.supportedInterfaces

def supportsCheckerFactory(self, factory):
        """
        Returns whether a checker factory will provide at least one of
        the credentials interfaces that we care about.
        """
        for interface in factory.credentialInterfaces:
            if self.supportsInterface(interface):
                return True
        return False

def addChecker(self, checker):
        """
        Supply a supplied credentials checker to the Options class.
        """
        # First figure out which interfaces we're willing to support.
        supported = []
        if self.supportedInterfaces is None:
            supported = checker.credentialInterfaces
        else:
            for interface in checker.credentialInterfaces:
                if self.supportsInterface(interface):
                    supported.append(interface)
        if not supported:
            raise UnsupportedInterfaces(checker.credentialInterfaces)
        # If we get this far, then we know we can use this checker.
        if "credInterfaces" not in self:
            self["credInterfaces"] = {}
        if "credCheckers" not in self:
            self["credCheckers"] = []
        self["credCheckers"].append(checker)
        for interface in supported:
            self["credInterfaces"].setdefault(interface, []).append(checker)

def opt_auth(self, description):
        """
        Specify an authentication method for the server.
        """
        try:
            self.addChecker(makeChecker(description))
        except UnsupportedInterfaces as e:
            raise usage.UsageError("Auth plugin not supported: %s" % e.args[0])
        except InvalidAuthType as e:
            raise usage.UsageError("Auth plugin not recognized: %s" % e.args[0])
        except Exception as e:
            raise usage.UsageError("Unexpected error: %s" % e)

def _checkerFactoriesForOptHelpAuth(self):
        """
        Return a list of which authTypes will be displayed by --help-auth.
        This makes it a lot easier to test this module.
        """
        for factory in findCheckerFactories():
            for interface in factory.credentialInterfaces:
                if self.supportsInterface(interface):
                    yield factory
                    break

def opt_help_auth(self):
        """
        Show all authentication methods available.
        """
        self.authOutput.write("Usage: --auth AuthType[:ArgString]\n")
        self.authOutput.write("For detailed help: --help-auth-type AuthType\n")
        self.authOutput.write("\n")
        # Figure out the right width for our columns
        firstLength = 0
        for factory in self._checkerFactoriesForOptHelpAuth():
            if len(factory.authType) > firstLength:
                firstLength = len(factory.authType)
        formatString = "  %%-%is\t%%s\n" % firstLength
        self.authOutput.write(formatString % ("AuthType", "ArgString format"))
        self.authOutput.write(formatString % ("========", "================"))
        for factory in self._checkerFactoriesForOptHelpAuth():
            self.authOutput.write(
                formatString % (factory.authType, factory.argStringFormat)
            )
        self.authOutput.write("\n")
        raise SystemExit(0)

def opt_help_auth_type(self, authType):
        """
        Show help for a particular authentication type.
        """
        try:
            cf = findCheckerFactory(authType)
        except InvalidAuthType:
            raise usage.UsageError("Invalid auth type: %s" % authType)
        self.authOutput.write("Usage: --auth %s[:ArgString]\n" % authType)
        self.authOutput.write("ArgString format: %s\n" % cf.argStringFormat)
        self.authOutput.write("\n")
        for line in cf.authHelp.strip().splitlines():
            self.authOutput.write("  %s\n" % line.rstrip())
        self.authOutput.write("\n")
        if not self.supportsCheckerFactory(cf):
            self.authOutput.write("  %s\n" % notSupportedWarning)
            self.authOutput.write("\n")
        raise SystemExit(0)

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