Module exchangelib.autodiscover.discovery.base
Expand source code
import abc
import logging
from urllib.parse import urlparse
import dns.name
import dns.resolver
from cached_property import threaded_cached_property
from ...errors import AutoDiscoverCircularRedirect, AutoDiscoverFailed, TransportError
from ...protocol import FailFast
from ...util import DummyResponse, get_domain, get_redirect_url
from ..cache import autodiscover_cache
from ..protocol import AutodiscoverProtocol
log = logging.getLogger(__name__)
DNS_LOOKUP_ERRORS = (
    dns.name.EmptyLabel,
    dns.resolver.NXDOMAIN,
    dns.resolver.NoAnswer,
    dns.resolver.NoNameservers,
)
class SrvRecord:
    """A container for autodiscover-related SRV records in DNS."""
    def __init__(self, priority, weight, port, srv):
        self.priority = priority
        self.weight = weight
        self.port = port
        self.srv = srv
    def __eq__(self, other):
        return all(getattr(self, k) == getattr(other, k) for k in self.__dict__)
class BaseAutodiscovery(metaclass=abc.ABCMeta):
    """Autodiscover is a Microsoft protocol for automatically getting the endpoint of the Exchange server and other
    connection-related settings holding the email address using only the email address, and username and password of the
    user.
    For a description of the protocol implemented, see "Autodiscover for Exchange ActiveSync developers":
    https://docs.microsoft.com/en-us/previous-versions/office/developer/exchange-server-interoperability-guidance/hh352638%28v%3dexchg.140%29
    Descriptions of the steps from the article are provided in their respective methods in this class.
    For a description of how to handle autodiscover error messages, see:
    https://docs.microsoft.com/en-us/exchange/client-developer/exchange-web-services/handling-autodiscover-error-messages
    A tip from the article:
    The client can perform steps 1 through 4 in any order or in parallel to expedite the process, but it must wait for
    responses to finish at each step before proceeding. Given that many organizations prefer to use the URL in step 2 to
    set up the Autodiscover service, the client might try this step first.
    Another possibly newer resource which has not yet been attempted is "Outlook 2016 Implementation of Autodiscover":
    https://support.microsoft.com/en-us/help/3211279/outlook-2016-implementation-of-autodiscover
    WARNING: The autodiscover protocol is very complicated. If you have problems autodiscovering using this
    implementation, start by doing an official test at https://testconnectivity.microsoft.com
    """
    # When connecting to servers that may not be serving the correct endpoint, we should use a retry policy that does
    # not leave us hanging for a long time on each step in the protocol.
    INITIAL_RETRY_POLICY = FailFast()
    RETRY_WAIT = 10  # Seconds to wait before retry on connection errors
    MAX_REDIRECTS = 10  # Maximum number of URL redirects before we give up
    DNS_RESOLVER_KWARGS = {}
    DNS_RESOLVER_ATTRS = {
        "timeout": AutodiscoverProtocol.TIMEOUT / 2.5,  # Timeout for query to a single nameserver
    }
    DNS_RESOLVER_LIFETIME = AutodiscoverProtocol.TIMEOUT  # Total timeout for a query in case of multiple nameservers
    URL_PATH = None
    def __init__(self, email, credentials=None):
        """
        :param email: The email address to autodiscover
        :param credentials: Credentials with authorization to make autodiscover lookups for this Account
            (Default value = None)
        """
        self.email = email
        self.credentials = credentials
        self._urls_visited = []  # Collects HTTP and Autodiscover redirects
        self._redirect_count = 0
        self._emails_visited = []  # Collects Autodiscover email redirects
    def discover(self):
        self._emails_visited.append(self.email.lower())
        # Check the autodiscover cache to see if we already know the autodiscover service endpoint for this email
        # domain. Use a lock to guard against multiple threads competing to cache information.
        log.debug("Waiting for autodiscover_cache lock")
        with autodiscover_cache:
            log.debug("autodiscover_cache lock acquired")
            cache_key = self._cache_key
            domain = get_domain(self.email)
            if cache_key in autodiscover_cache:
                ad_protocol = autodiscover_cache[cache_key]
                log.debug("Cache hit for key %s: %s", cache_key, ad_protocol.service_endpoint)
                try:
                    ad = self._quick(protocol=ad_protocol)
                except AutoDiscoverFailed:
                    # Autodiscover no longer works with this domain. Clear cache and try again after releasing the lock
                    log.debug("AD request failure. Removing cache for key %s", cache_key)
                    del autodiscover_cache[cache_key]
                    ad = self._step_1(hostname=domain)
            else:
                # This will cache the result
                log.debug("Cache miss for key %s", cache_key)
                ad = self._step_1(hostname=domain)
        log.debug("Released autodiscover_cache_lock")
        if ad.redirect_address:
            log.debug("Got a redirect address: %s", ad.redirect_address)
            if ad.redirect_address.lower() in self._emails_visited:
                raise AutoDiscoverCircularRedirect("We were redirected to an email address we have already seen")
            # Start over, but with the new email address
            self.email = ad.redirect_address
            return self.discover()
        # We successfully received a response. Clear the cache of seen emails etc.
        self.clear()
        return self._build_response(ad_response=ad)
    def clear(self):
        # This resets cached variables
        self._urls_visited = []
        self._redirect_count = 0
        self._emails_visited = []
    @property
    def _cache_key(self):
        # We may be using multiple different credentials and changing our minds on TLS verification. This key
        # combination should be safe for caching.
        domain = get_domain(self.email)
        return domain, self.credentials
    @threaded_cached_property
    def resolver(self):
        resolver = dns.resolver.Resolver(**self.DNS_RESOLVER_KWARGS)
        for k, v in self.DNS_RESOLVER_ATTRS.items():
            setattr(resolver, k, v)
        return resolver
    @abc.abstractmethod
    def _build_response(self, ad_response):
        pass
    @abc.abstractmethod
    def _quick(self, protocol):
        pass
    def _redirect_url_is_valid(self, url):
        """Three separate responses can be “Redirect responses”:
        * An HTTP status code (301, 302) with a new URL
        * An HTTP status code of 200, but with a payload XML containing a redirect to a different URL
        * An HTTP status code of 200, but with a payload XML containing a different SMTP address as the target address
        We only handle the HTTP 302 redirects here. We validate the URL received in the redirect response to ensure that
        it does not redirect to non-SSL endpoints or SSL endpoints with invalid certificates, and that the redirect is
        not circular. Finally, we should fail after 10 redirects.
        :param url:
        :return:
        """
        if url.lower() in self._urls_visited:
            log.warning("We have already tried this URL: %s", url)
            return False
        if self._redirect_count >= self.MAX_REDIRECTS:
            log.warning("We reached max redirects at URL: %s", url)
            return False
        # We require TLS endpoints
        if not url.startswith("https://"):
            log.debug("Invalid scheme for URL: %s", url)
            return False
        # Quick test that the endpoint responds and that TLS handshake is OK
        try:
            self._get_unauthenticated_response(url, method="head")
        except TransportError as e:
            log.debug("Response error on redirect URL %s: %s", url, e)
            return False
        self._redirect_count += 1
        return True
    @abc.abstractmethod
    def _get_unauthenticated_response(self, url, method="post"):
        pass
    @abc.abstractmethod
    def _attempt_response(self, url):
        pass
    def _ensure_valid_hostname(self, url):
        hostname = urlparse(url).netloc
        log.debug("Checking if %s can be looked up in DNS", hostname)
        try:
            self.resolver.resolve(f"{hostname}.", "A", lifetime=self.DNS_RESOLVER_LIFETIME)
        except DNS_LOOKUP_ERRORS as e:
            log.debug("DNS A lookup failure: %s", e)
            # 'requests' is bad at reporting that a hostname cannot be resolved. Let's check this separately.
            # Don't retry on DNS errors. They will most likely be persistent.
            raise TransportError(f"{hostname!r} has no DNS entry")
    def _get_srv_records(self, hostname):
        """Send a DNS query for SRV entries for the hostname.
        An SRV entry that has been formatted for autodiscovery will have the following format:
            canonical name = mail.example.com.
            service = 8 100 443 webmail.example.com.
        The first three numbers in the service line are: priority, weight, port
        :param hostname:
        :return:
        """
        log.debug("Attempting to get SRV records for %s", hostname)
        records = []
        try:
            answers = self.resolver.resolve(f"{hostname}.", "SRV", lifetime=self.DNS_RESOLVER_LIFETIME)
        except DNS_LOOKUP_ERRORS as e:
            log.debug("DNS SRV lookup failure: %s", e)
            return records
        for rdata in answers:
            try:
                vals = rdata.to_text().strip().rstrip(".").split(" ")
                # Raise ValueError if the first three are not ints, and IndexError if there are less than 4 values
                priority, weight, port, srv = int(vals[0]), int(vals[1]), int(vals[2]), vals[3]
                record = SrvRecord(priority=priority, weight=weight, port=port, srv=srv)
                log.debug("Found SRV record %s ", record)
                records.append(record)
            except (ValueError, IndexError):
                log.debug("Incompatible SRV record for %s (%s)", hostname, rdata.to_text())
        return records
    def _step_1(self, hostname):
        """Perform step 1, where the client sends an Autodiscover request to
        https://example.com/ and then does one of the following:
            * If the Autodiscover attempt succeeds, the client proceeds to step 5.
            * If the Autodiscover attempt fails, the client proceeds to step 2.
        :param hostname:
        :return:
        """
        url = f"https://{hostname}/{self.URL_PATH}"
        log.info("Step 1: Trying autodiscover on %r with email %r", url, self.email)
        is_valid_response, ad = self._attempt_response(url=url)
        if is_valid_response:
            return self._step_5(ad=ad)
        return self._step_2(hostname=hostname)
    def _step_2(self, hostname):
        """Perform step 2, where the client sends an Autodiscover request to
        https://autodiscover.example.com/ and then does one of the following:
            * If the Autodiscover attempt succeeds, the client proceeds to step 5.
            * If the Autodiscover attempt fails, the client proceeds to step 3.
        :param hostname:
        :return:
        """
        url = f"https://autodiscover.{hostname}/{self.URL_PATH}"
        log.info("Step 2: Trying autodiscover on %r with email %r", url, self.email)
        is_valid_response, ad = self._attempt_response(url=url)
        if is_valid_response:
            return self._step_5(ad=ad)
        return self._step_3(hostname=hostname)
    def _step_3(self, hostname):
        """Perform step 3, where the client sends an unauthenticated GET method request to
        http://autodiscover.example.com/ (Note that this is a non-HTTPS endpoint). The
        client then does one of the following:
            * If the GET request returns a 302 redirect response, it gets the redirection URL from the 'Location' HTTP
            header and validates it as described in the "Redirect responses" section. The client then does one of the
            following:
                * If the redirection URL is valid, the client tries the URL and then does one of the following:
                    * If the attempt succeeds, the client proceeds to step 5.
                    * If the attempt fails, the client proceeds to step 4.
                * If the redirection URL is not valid, the client proceeds to step 4.
            * If the GET request does not return a 302 redirect response, the client proceeds to step 4.
        :param hostname:
        :return:
        """
        url = f"http://autodiscover.{hostname}/{self.URL_PATH}"
        log.info("Step 3: Trying autodiscover on %r with email %r", url, self.email)
        try:
            _, r = self._get_unauthenticated_response(url=url, method="get")
        except TransportError:
            r = DummyResponse(url=url)
        if r.status_code in (301, 302) and "location" in r.headers:
            redirect_url = get_redirect_url(r)
            if self._redirect_url_is_valid(url=redirect_url):
                is_valid_response, ad = self._attempt_response(url=redirect_url)
                if is_valid_response:
                    return self._step_5(ad=ad)
                log.debug("Got invalid response")
                return self._step_4(hostname=hostname)
            log.debug("Got invalid redirect URL")
            return self._step_4(hostname=hostname)
        log.debug("Got no redirect URL")
        return self._step_4(hostname=hostname)
    def _step_4(self, hostname):
        """Perform step 4, where the client performs a Domain Name System (DNS) query for an SRV record for
        _autodiscover._tcp.example.com. The query might return multiple records. The client selects only records that
        point to an SSL endpoint and that have the highest priority and weight. One of the following actions then
        occurs:
            * If no such records are returned, the client proceeds to step 6.
            * If records are returned, the application randomly chooses a record in the list and validates the endpoint
              that it points to by following the process described in the "Redirect Response" section. The client then
              does one of the following:
                * If the redirection URL is valid, the client tries the URL and then does one of the following:
                    * If the attempt succeeds, the client proceeds to step 5.
                    * If the attempt fails, the client proceeds to step 6.
                * If the redirection URL is not valid, the client proceeds to step 6.
        :param hostname:
        :return:
        """
        dns_hostname = f"_autodiscover._tcp.{hostname}"
        log.info("Step 4: Trying autodiscover on %r with email %r", dns_hostname, self.email)
        srv_records = self._get_srv_records(dns_hostname)
        try:
            srv_host = _select_srv_host(srv_records)
        except ValueError:
            srv_host = None
        if not srv_host:
            return self._step_6()
        redirect_url = f"https://{srv_host}/{self.URL_PATH}"
        if self._redirect_url_is_valid(url=redirect_url):
            is_valid_response, ad = self._attempt_response(url=redirect_url)
            if is_valid_response:
                return self._step_5(ad=ad)
            log.debug("Got invalid response")
            return self._step_6()
        log.debug("Got invalid redirect URL")
        return self._step_6()
    def _step_5(self, ad):
        """Perform step 5. When a valid Autodiscover request succeeds, the following sequence occurs:
            * If the server responds with an HTTP 302 redirect, the client validates the redirection URL according to
              the process defined in the "Redirect responses" and then does one of the following:
                * If the redirection URL is valid, the client tries the URL and then does one of the following:
                    * If the attempt succeeds, the client repeats step 5 from the beginning.
                    * If the attempt fails, the client proceeds to step 6.
                * If the redirection URL is not valid, the client proceeds to step 6.
            * If the server responds with a valid Autodiscover response, the client does one of the following:
                * If the value of the Action element is "Redirect", the client gets the redirection email address from
                  the Redirect element and then returns to step 1, using this new email address.
                * If the value of the Action element is "Settings", the client has successfully received the requested
                  configuration settings for the specified user. The client does not need to proceed to step 6.
        :param ad:
        :return:
        """
        log.info("Step 5: Checking response")
        # This is not explicit in the protocol, but let's raise any errors here
        ad.raise_errors()
        if hasattr(ad, "response"):
            # Hack for PoxAutodiscover
            ad = ad.response
        if ad.redirect_url:
            log.debug("Got a redirect URL: %s", ad.redirect_url)
            # We are diverging a bit from the protocol here. We will never get an HTTP 302 since earlier steps already
            # followed the redirects where possible. Instead, we handle redirect responses here.
            if self._redirect_url_is_valid(url=ad.redirect_url):
                is_valid_response, ad = self._attempt_response(url=ad.redirect_url)
                if is_valid_response:
                    return self._step_5(ad=ad)
                log.debug("Got invalid response")
                return self._step_6()
            log.debug("Invalid redirect URL")
            return self._step_6()
        # This could be an email redirect. Let outer layer handle this
        return ad
    def _step_6(self):
        """Perform step 6. If the client cannot contact the Autodiscover service, the client should ask the user for
        the Exchange server name and use it to construct an Exchange EWS URL. The client should try to use this URL for
        future requests.
        """
        raise AutoDiscoverFailed(
            f"All steps in the autodiscover protocol failed for email {self.email}. If you think this is an error, "
            f"consider doing an official test at https://testconnectivity.microsoft.com"
        )
def _select_srv_host(srv_records):
    """Select the record with the highest priority, that also supports TLS.
    :param srv_records:
    :return:
    """
    best_record = None
    for srv_record in srv_records:
        if srv_record.port != 443:
            log.debug("Skipping SRV record %r (no TLS)", srv_record)
            continue
        # Assume port 443 will serve TLS. If not, autodiscover will probably also be broken for others.
        if best_record is None or best_record.priority < srv_record.priority:
            best_record = srv_record
    if not best_record:
        raise ValueError("No suitable records")
    return best_record.srvClasses
- class BaseAutodiscovery (email, credentials=None)
- 
Autodiscover is a Microsoft protocol for automatically getting the endpoint of the Exchange server and other connection-related settings holding the email address using only the email address, and username and password of the user. For a description of the protocol implemented, see "Autodiscover for Exchange ActiveSync developers": Descriptions of the steps from the article are provided in their respective methods in this class. For a description of how to handle autodiscover error messages, see: A tip from the article: The client can perform steps 1 through 4 in any order or in parallel to expedite the process, but it must wait for responses to finish at each step before proceeding. Given that many organizations prefer to use the URL in step 2 to set up the Autodiscover service, the client might try this step first. Another possibly newer resource which has not yet been attempted is "Outlook 2016 Implementation of Autodiscover": https://support.microsoft.com/en-us/help/3211279/outlook-2016-implementation-of-autodiscover WARNING: The autodiscover protocol is very complicated. If you have problems autodiscovering using this implementation, start by doing an official test at https://testconnectivity.microsoft.com :param email: The email address to autodiscover :param credentials: Credentials with authorization to make autodiscover lookups for this Account (Default value = None) Expand source codeclass BaseAutodiscovery(metaclass=abc.ABCMeta): """Autodiscover is a Microsoft protocol for automatically getting the endpoint of the Exchange server and other connection-related settings holding the email address using only the email address, and username and password of the user. For a description of the protocol implemented, see "Autodiscover for Exchange ActiveSync developers": https://docs.microsoft.com/en-us/previous-versions/office/developer/exchange-server-interoperability-guidance/hh352638%28v%3dexchg.140%29 Descriptions of the steps from the article are provided in their respective methods in this class. For a description of how to handle autodiscover error messages, see: https://docs.microsoft.com/en-us/exchange/client-developer/exchange-web-services/handling-autodiscover-error-messages A tip from the article: The client can perform steps 1 through 4 in any order or in parallel to expedite the process, but it must wait for responses to finish at each step before proceeding. Given that many organizations prefer to use the URL in step 2 to set up the Autodiscover service, the client might try this step first. Another possibly newer resource which has not yet been attempted is "Outlook 2016 Implementation of Autodiscover": https://support.microsoft.com/en-us/help/3211279/outlook-2016-implementation-of-autodiscover WARNING: The autodiscover protocol is very complicated. If you have problems autodiscovering using this implementation, start by doing an official test at https://testconnectivity.microsoft.com """ # When connecting to servers that may not be serving the correct endpoint, we should use a retry policy that does # not leave us hanging for a long time on each step in the protocol. INITIAL_RETRY_POLICY = FailFast() RETRY_WAIT = 10 # Seconds to wait before retry on connection errors MAX_REDIRECTS = 10 # Maximum number of URL redirects before we give up DNS_RESOLVER_KWARGS = {} DNS_RESOLVER_ATTRS = { "timeout": AutodiscoverProtocol.TIMEOUT / 2.5, # Timeout for query to a single nameserver } DNS_RESOLVER_LIFETIME = AutodiscoverProtocol.TIMEOUT # Total timeout for a query in case of multiple nameservers URL_PATH = None def __init__(self, email, credentials=None): """ :param email: The email address to autodiscover :param credentials: Credentials with authorization to make autodiscover lookups for this Account (Default value = None) """ self.email = email self.credentials = credentials self._urls_visited = [] # Collects HTTP and Autodiscover redirects self._redirect_count = 0 self._emails_visited = [] # Collects Autodiscover email redirects def discover(self): self._emails_visited.append(self.email.lower()) # Check the autodiscover cache to see if we already know the autodiscover service endpoint for this email # domain. Use a lock to guard against multiple threads competing to cache information. log.debug("Waiting for autodiscover_cache lock") with autodiscover_cache: log.debug("autodiscover_cache lock acquired") cache_key = self._cache_key domain = get_domain(self.email) if cache_key in autodiscover_cache: ad_protocol = autodiscover_cache[cache_key] log.debug("Cache hit for key %s: %s", cache_key, ad_protocol.service_endpoint) try: ad = self._quick(protocol=ad_protocol) except AutoDiscoverFailed: # Autodiscover no longer works with this domain. Clear cache and try again after releasing the lock log.debug("AD request failure. Removing cache for key %s", cache_key) del autodiscover_cache[cache_key] ad = self._step_1(hostname=domain) else: # This will cache the result log.debug("Cache miss for key %s", cache_key) ad = self._step_1(hostname=domain) log.debug("Released autodiscover_cache_lock") if ad.redirect_address: log.debug("Got a redirect address: %s", ad.redirect_address) if ad.redirect_address.lower() in self._emails_visited: raise AutoDiscoverCircularRedirect("We were redirected to an email address we have already seen") # Start over, but with the new email address self.email = ad.redirect_address return self.discover() # We successfully received a response. Clear the cache of seen emails etc. self.clear() return self._build_response(ad_response=ad) def clear(self): # This resets cached variables self._urls_visited = [] self._redirect_count = 0 self._emails_visited = [] @property def _cache_key(self): # We may be using multiple different credentials and changing our minds on TLS verification. This key # combination should be safe for caching. domain = get_domain(self.email) return domain, self.credentials @threaded_cached_property def resolver(self): resolver = dns.resolver.Resolver(**self.DNS_RESOLVER_KWARGS) for k, v in self.DNS_RESOLVER_ATTRS.items(): setattr(resolver, k, v) return resolver @abc.abstractmethod def _build_response(self, ad_response): pass @abc.abstractmethod def _quick(self, protocol): pass def _redirect_url_is_valid(self, url): """Three separate responses can be “Redirect responses”: * An HTTP status code (301, 302) with a new URL * An HTTP status code of 200, but with a payload XML containing a redirect to a different URL * An HTTP status code of 200, but with a payload XML containing a different SMTP address as the target address We only handle the HTTP 302 redirects here. We validate the URL received in the redirect response to ensure that it does not redirect to non-SSL endpoints or SSL endpoints with invalid certificates, and that the redirect is not circular. Finally, we should fail after 10 redirects. :param url: :return: """ if url.lower() in self._urls_visited: log.warning("We have already tried this URL: %s", url) return False if self._redirect_count >= self.MAX_REDIRECTS: log.warning("We reached max redirects at URL: %s", url) return False # We require TLS endpoints if not url.startswith("https://"): log.debug("Invalid scheme for URL: %s", url) return False # Quick test that the endpoint responds and that TLS handshake is OK try: self._get_unauthenticated_response(url, method="head") except TransportError as e: log.debug("Response error on redirect URL %s: %s", url, e) return False self._redirect_count += 1 return True @abc.abstractmethod def _get_unauthenticated_response(self, url, method="post"): pass @abc.abstractmethod def _attempt_response(self, url): pass def _ensure_valid_hostname(self, url): hostname = urlparse(url).netloc log.debug("Checking if %s can be looked up in DNS", hostname) try: self.resolver.resolve(f"{hostname}.", "A", lifetime=self.DNS_RESOLVER_LIFETIME) except DNS_LOOKUP_ERRORS as e: log.debug("DNS A lookup failure: %s", e) # 'requests' is bad at reporting that a hostname cannot be resolved. Let's check this separately. # Don't retry on DNS errors. They will most likely be persistent. raise TransportError(f"{hostname!r} has no DNS entry") def _get_srv_records(self, hostname): """Send a DNS query for SRV entries for the hostname. An SRV entry that has been formatted for autodiscovery will have the following format: canonical name = mail.example.com. service = 8 100 443 webmail.example.com. The first three numbers in the service line are: priority, weight, port :param hostname: :return: """ log.debug("Attempting to get SRV records for %s", hostname) records = [] try: answers = self.resolver.resolve(f"{hostname}.", "SRV", lifetime=self.DNS_RESOLVER_LIFETIME) except DNS_LOOKUP_ERRORS as e: log.debug("DNS SRV lookup failure: %s", e) return records for rdata in answers: try: vals = rdata.to_text().strip().rstrip(".").split(" ") # Raise ValueError if the first three are not ints, and IndexError if there are less than 4 values priority, weight, port, srv = int(vals[0]), int(vals[1]), int(vals[2]), vals[3] record = SrvRecord(priority=priority, weight=weight, port=port, srv=srv) log.debug("Found SRV record %s ", record) records.append(record) except (ValueError, IndexError): log.debug("Incompatible SRV record for %s (%s)", hostname, rdata.to_text()) return records def _step_1(self, hostname): """Perform step 1, where the client sends an Autodiscover request to https://example.com/ and then does one of the following: * If the Autodiscover attempt succeeds, the client proceeds to step 5. * If the Autodiscover attempt fails, the client proceeds to step 2. :param hostname: :return: """ url = f"https://{hostname}/{self.URL_PATH}" log.info("Step 1: Trying autodiscover on %r with email %r", url, self.email) is_valid_response, ad = self._attempt_response(url=url) if is_valid_response: return self._step_5(ad=ad) return self._step_2(hostname=hostname) def _step_2(self, hostname): """Perform step 2, where the client sends an Autodiscover request to https://autodiscover.example.com/ and then does one of the following: * If the Autodiscover attempt succeeds, the client proceeds to step 5. * If the Autodiscover attempt fails, the client proceeds to step 3. :param hostname: :return: """ url = f"https://autodiscover.{hostname}/{self.URL_PATH}" log.info("Step 2: Trying autodiscover on %r with email %r", url, self.email) is_valid_response, ad = self._attempt_response(url=url) if is_valid_response: return self._step_5(ad=ad) return self._step_3(hostname=hostname) def _step_3(self, hostname): """Perform step 3, where the client sends an unauthenticated GET method request to http://autodiscover.example.com/ (Note that this is a non-HTTPS endpoint). The client then does one of the following: * If the GET request returns a 302 redirect response, it gets the redirection URL from the 'Location' HTTP header and validates it as described in the "Redirect responses" section. The client then does one of the following: * If the redirection URL is valid, the client tries the URL and then does one of the following: * If the attempt succeeds, the client proceeds to step 5. * If the attempt fails, the client proceeds to step 4. * If the redirection URL is not valid, the client proceeds to step 4. * If the GET request does not return a 302 redirect response, the client proceeds to step 4. :param hostname: :return: """ url = f"http://autodiscover.{hostname}/{self.URL_PATH}" log.info("Step 3: Trying autodiscover on %r with email %r", url, self.email) try: _, r = self._get_unauthenticated_response(url=url, method="get") except TransportError: r = DummyResponse(url=url) if r.status_code in (301, 302) and "location" in r.headers: redirect_url = get_redirect_url(r) if self._redirect_url_is_valid(url=redirect_url): is_valid_response, ad = self._attempt_response(url=redirect_url) if is_valid_response: return self._step_5(ad=ad) log.debug("Got invalid response") return self._step_4(hostname=hostname) log.debug("Got invalid redirect URL") return self._step_4(hostname=hostname) log.debug("Got no redirect URL") return self._step_4(hostname=hostname) def _step_4(self, hostname): """Perform step 4, where the client performs a Domain Name System (DNS) query for an SRV record for _autodiscover._tcp.example.com. The query might return multiple records. The client selects only records that point to an SSL endpoint and that have the highest priority and weight. One of the following actions then occurs: * If no such records are returned, the client proceeds to step 6. * If records are returned, the application randomly chooses a record in the list and validates the endpoint that it points to by following the process described in the "Redirect Response" section. The client then does one of the following: * If the redirection URL is valid, the client tries the URL and then does one of the following: * If the attempt succeeds, the client proceeds to step 5. * If the attempt fails, the client proceeds to step 6. * If the redirection URL is not valid, the client proceeds to step 6. :param hostname: :return: """ dns_hostname = f"_autodiscover._tcp.{hostname}" log.info("Step 4: Trying autodiscover on %r with email %r", dns_hostname, self.email) srv_records = self._get_srv_records(dns_hostname) try: srv_host = _select_srv_host(srv_records) except ValueError: srv_host = None if not srv_host: return self._step_6() redirect_url = f"https://{srv_host}/{self.URL_PATH}" if self._redirect_url_is_valid(url=redirect_url): is_valid_response, ad = self._attempt_response(url=redirect_url) if is_valid_response: return self._step_5(ad=ad) log.debug("Got invalid response") return self._step_6() log.debug("Got invalid redirect URL") return self._step_6() def _step_5(self, ad): """Perform step 5. When a valid Autodiscover request succeeds, the following sequence occurs: * If the server responds with an HTTP 302 redirect, the client validates the redirection URL according to the process defined in the "Redirect responses" and then does one of the following: * If the redirection URL is valid, the client tries the URL and then does one of the following: * If the attempt succeeds, the client repeats step 5 from the beginning. * If the attempt fails, the client proceeds to step 6. * If the redirection URL is not valid, the client proceeds to step 6. * If the server responds with a valid Autodiscover response, the client does one of the following: * If the value of the Action element is "Redirect", the client gets the redirection email address from the Redirect element and then returns to step 1, using this new email address. * If the value of the Action element is "Settings", the client has successfully received the requested configuration settings for the specified user. The client does not need to proceed to step 6. :param ad: :return: """ log.info("Step 5: Checking response") # This is not explicit in the protocol, but let's raise any errors here ad.raise_errors() if hasattr(ad, "response"): # Hack for PoxAutodiscover ad = ad.response if ad.redirect_url: log.debug("Got a redirect URL: %s", ad.redirect_url) # We are diverging a bit from the protocol here. We will never get an HTTP 302 since earlier steps already # followed the redirects where possible. Instead, we handle redirect responses here. if self._redirect_url_is_valid(url=ad.redirect_url): is_valid_response, ad = self._attempt_response(url=ad.redirect_url) if is_valid_response: return self._step_5(ad=ad) log.debug("Got invalid response") return self._step_6() log.debug("Invalid redirect URL") return self._step_6() # This could be an email redirect. Let outer layer handle this return ad def _step_6(self): """Perform step 6. If the client cannot contact the Autodiscover service, the client should ask the user for the Exchange server name and use it to construct an Exchange EWS URL. The client should try to use this URL for future requests. """ raise AutoDiscoverFailed( f"All steps in the autodiscover protocol failed for email {self.email}. If you think this is an error, " f"consider doing an official test at https://testconnectivity.microsoft.com" )SubclassesClass variables- var DNS_RESOLVER_ATTRS
- var DNS_RESOLVER_KWARGS
- var DNS_RESOLVER_LIFETIME
- var INITIAL_RETRY_POLICY
- var MAX_REDIRECTS
- var RETRY_WAIT
- var URL_PATH
 Instance variables- var resolver
- 
Expand source codedef __get__(self, obj, cls): if obj is None: return self obj_dict = obj.__dict__ name = self.func.__name__ with self.lock: try: # check if the value was computed before the lock was acquired return obj_dict[name] except KeyError: # if not, do the calculation and release the lock return obj_dict.setdefault(name, self.func(obj))
 Methods- def clear(self)
- 
Expand source codedef clear(self): # This resets cached variables self._urls_visited = [] self._redirect_count = 0 self._emails_visited = []
- def discover(self)
- 
Expand source codedef discover(self): self._emails_visited.append(self.email.lower()) # Check the autodiscover cache to see if we already know the autodiscover service endpoint for this email # domain. Use a lock to guard against multiple threads competing to cache information. log.debug("Waiting for autodiscover_cache lock") with autodiscover_cache: log.debug("autodiscover_cache lock acquired") cache_key = self._cache_key domain = get_domain(self.email) if cache_key in autodiscover_cache: ad_protocol = autodiscover_cache[cache_key] log.debug("Cache hit for key %s: %s", cache_key, ad_protocol.service_endpoint) try: ad = self._quick(protocol=ad_protocol) except AutoDiscoverFailed: # Autodiscover no longer works with this domain. Clear cache and try again after releasing the lock log.debug("AD request failure. Removing cache for key %s", cache_key) del autodiscover_cache[cache_key] ad = self._step_1(hostname=domain) else: # This will cache the result log.debug("Cache miss for key %s", cache_key) ad = self._step_1(hostname=domain) log.debug("Released autodiscover_cache_lock") if ad.redirect_address: log.debug("Got a redirect address: %s", ad.redirect_address) if ad.redirect_address.lower() in self._emails_visited: raise AutoDiscoverCircularRedirect("We were redirected to an email address we have already seen") # Start over, but with the new email address self.email = ad.redirect_address return self.discover() # We successfully received a response. Clear the cache of seen emails etc. self.clear() return self._build_response(ad_response=ad)
 
- class SrvRecord (priority, weight, port, srv)
- 
A container for autodiscover-related SRV records in DNS. Expand source codeclass SrvRecord: """A container for autodiscover-related SRV records in DNS.""" def __init__(self, priority, weight, port, srv): self.priority = priority self.weight = weight self.port = port self.srv = srv def __eq__(self, other): return all(getattr(self, k) == getattr(other, k) for k in self.__dict__)