res_pjsip: Add ability to identify by Authorization username

A feature of chan_sip that service providers relied upon was the ability to
identify by the Authorization username.  This is most often used when customers
have a PBX that needs to register rather than identify by IP address.  From my
own experiance, this is pretty common with small businesses who otherwise
don't need a static IP.

In this scenario, a register from the customer's PBX may succeed because From
will usually contain the PBXs account id but an INVITE will contain the caller
id.  With nothing recognizable in From, the service provider's Asterisk can
never match to an endpoint and the INVITE just stays unauthorized.

The fixes:

A new value "auth_username" has been added to endpoint/identify_by that
will use the username and digest fields in the Authorization header
instead of username and domain in the the From header to match an endpoint,
or the To header to match an aor.  This code as added to
res_pjsip_endpoint_identifier_user rather than creating a new module.

Although identify_by was always a comma-separated list, there was only
1 choice so order wasn't preserved.  So to keep the order, a vector was added
to the end of ast_sip_endpoint.  This is only used by res_pjsip_registrar
to find the aor.  The res_pjsip_endpoint_identifier_* modules are called in
globals/endpoint_identifier_order.

Along the way, the logic in res_pjsip_registrar was corrected to match
most-specific to least-specific as res_pjsip_endpoint_identifier_user does.

The order is:

username@domain
username@domain_alias
username

Auth by username does present 1 problem however, the first INVITE won't have
an Authorization header so the distributor, not finding a match on anything,
sends a securty_alert.  It still sends a 401 with a challenge so the next
INVITE will have the Authorization header and presumably succeed.  As a result
though, that first security alert is actually a false alarm.

To address this, a new feature has been added to pjsip_distributor that keeps
track of unidentified requests and only sends the security alert if a
configurable number of unidentified requests come from the same IP in a
configurable amout of time.  Those configuration options have been added to
the global config object.  This feature is only used when auth_username
is enabled.

Finally, default_realm was added to the globals object to replace the hard
coded "asterisk" used when an endpoint is not yet identified.

The testsuite tests all pass but new tests are forthcoming for this new
feature.

ASTERISK-25835 #close
Reported-by: Ross Beer

Change-Id: I30ba62d208e6f63439600916fcd1c08a365ed69d

1 files changed, 64 insertions, 7 deletions

diff --git a/res/res_pjsip.c b/res/res_pjsip.c
index daab0af3f..6890e637b 100644
--- a/res/res_pjsip.c
+++ b/res/res_pjsip.c
@@ -252,18 +252,35 @@
 				<configOption name="identify_by" default="username,location">
 					<synopsis>Way(s) for Endpoint to be identified</synopsis>
 					<description><para>
-						An endpoint can be identified in multiple ways. Currently, the only supported
-						option is <literal>username</literal>, which matches the endpoint based on the
-						username in the From header.
+						Endpoints and aors can be identified in multiple ways. Currently, the supported
+						options are <literal>username</literal>, which matches the endpoint or aor id based on
+						the username and domain in the From header (or To header for aors), and
+						<literal>auth_username</literal>, which matches the endpoint or aor id based on the
+						username and realm in the Authentication header.  In all cases, if an exact match
+						on both username and domain/realm fails, the match will be retried with just the username.
 						</para>
+						<note><para>
+						Identification by auth_username has some security considerations because an
+						Authentication header is not present on the first message of a dialog when
+						digest authentication is used.  The client can't generate it until the server
+						sends the challenge in a 401 response.  Since Asterisk normally sends a security
+						event when an incoming request can't be matched to an endpoint, using auth_username
+						requires that the security event be deferred until a request is received with
+						the Authentication header and only generated if the username doesn't result in a
+						match.  This may result in a delay before an attack is recognized.  You can control
+						how many unmatched requests are received from a single ip address before a security
+						event is generated using the unidentified_request parameters in the "global"
+						configuration object.
+						</para></note>
 						<note><para>Endpoints can also be identified by IP address; however, that method
 						of identification is not handled by this configuration option. See the documentation
 						for the <literal>identify</literal> configuration section for more details on that
-						method of endpoint identification. If this option is set to <literal>username</literal>
-						and an <literal>identify</literal> configuration section exists for the endpoint, then
-						the endpoint can be identified in multiple ways.</para></note>
+						method of endpoint identification. If this option is set and an <literal>identify</literal>
+						configuration section exists for the endpoint, then the endpoint can be identified in
+						multiple ways.</para></note>
 						<enumlist>
 							<enum name="username" />
+							<enum name="auth_username" />
 						</enumlist>
 					</description>
 				</configOption>
@@ -1304,6 +1321,24 @@
 					<synopsis>The maximum amount of time from startup that qualifies should be attempted on all contacts.
 					If greater than the qualify_frequency for an aor, qualify_frequency will be used instead.</synopsis>
 				</configOption>
+				<configOption name="unidentified_request_period" default="5">
+					<synopsis>The number of seconds over which to accumulate unidentified requests.</synopsis>
+					<description><para>
+					If <literal>unidentified_request_count</literal> unidentified requests are received
+					during <literal>unidentified_request_period</literal>, a security event will be generated.
+					</para></description>
+				</configOption>
+				<configOption name="unidentified_request_count" default="5">
+					<synopsis>The number of unidentified requests from a single IP to allow.</synopsis>
+					<description><para>
+					If <literal>unidentified_request_count</literal> unidentified requests are received
+					during <literal>unidentified_request_period</literal>, a security event will be generated.
+					</para></description>
+				</configOption>
+				<configOption name="unidentified_request_prune_interval" default="30">
+					<synopsis>The interval at which unidentified requests are older than
+					twice the unidentified_request_period are pruned.</synopsis>
+				</configOption>
 				<configOption name="type">
 					<synopsis>Must be of type 'global'.</synopsis>
 				</configOption>
@@ -1327,13 +1362,35 @@
 				<configOption name="endpoint_identifier_order" default="ip,username,anonymous">
 					<synopsis>The order by which endpoint identifiers are processed and checked.
                                         Identifier names are usually derived from and can be found in the endpoint
-                                        identifier module itself (res_pjsip_endpoint_identifier_*)</synopsis>
+                                        identifier module itself (res_pjsip_endpoint_identifier_*).
+                                        You can use the CLI command "pjsip show identifiers" to see the
+                                        identifiers currently available.</synopsis>
+                    <description>
+						<note><para>
+						One of the identifiers is "auth_username" which matches on the username in
+						an Authentication header.  This method has some security considerations because an
+						Authentication header is not present on the first message of a dialog when
+						digest authentication is used.  The client can't generate it until the server
+						sends the challenge in a 401 response.  Since Asterisk normally sends a security
+						event when an incoming request can't be matched to an endpoint, using auth_username
+						requires that the security event be deferred until a request is received with
+						the Authentication header and only generated if the username doesn't result in a
+						match.  This may result in a delay before an attack is recognized.  You can control
+						how many unmatched requests are received from a single ip address before a security
+						event is generated using the unidentified_request parameters.
+						</para></note>
+                    </description>
 				</configOption>
 				<configOption name="default_from_user" default="asterisk">
 					<synopsis>When Asterisk generates an outgoing SIP request, the From header username will be
                                         set to this value if there is no better option (such as CallerID) to be
                                         used.</synopsis>
 				</configOption>
+				<configOption name="default_realm" default="asterisk">
+					<synopsis>When Asterisk generates an challenge, the digest will be
+                                        set to this value if there is no better option (such as auth/realm) to be
+                                        used.</synopsis>
+				</configOption>
 			</configObject>
 		</configFile>
 	</configInfo>