Remove format constraint of client id

Describe Zaqar how to remove the format constraint of
client id.

Change-Id: Ibb551d33cb4148c5ff3344a23467e4055fe6ba89
Implements: blueprint remove-format-constraint-of-client-id

specs/rocky/remove-format-contraint-of-client-id.rst

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+..
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+
+====================================
+Remove format constraint of client id
+====================================
+
+https://blueprints.launchpad.net/zaqar/+spec/remove-format-constraint-of-client-id
+
+Since some clients use different format of client id not only uuid,
+so Zaqar will support this function. This also requires user to ensure the
+client id is immutable.
+
+
+Problem description
+===================
+
+Now Zaqar has format constraint to client id, must be UUID format. But this
+constraint is not very reasonable under some cases, like user want to use
+user id in LDAP as client id, but Zaqar doesn't allow this now.
+
+
+Proposed change
+===============
+* Add Three config options::
+
+  # 'client_id_uuid_safe': Defines the format of client id, the value could be
+    "strict" or "off". "strict" means the format of client id must be uuid,
+    "off" means the restriction be removed. The default value is 'strict'.
+  # 'min_length_client_id': Defines the minimum length of client id if remove
+    the uuid restriction. Default value is 10.
+  # 'max_length_client_id': Defines the maximum length of client id if
+    remove the uuid restriction. Default value is 36.
+
+* Will change the method 'require_client_id' in wsgi/helpers.py to support
+  validating the different format of client id.
+
+API Impact
+-----------
+For WSGI: Will impact all APIs in v1.1 and v2 version.
+
+For WebSocket: Will impact message list and message post in v2 version. And we
+will support others APIs in following patch.
+
+Drawbacks
+---------
+There may be a tiny performance impact when user uses very long client id since
+Zaqar need to store the client id in storage layer.
+
+
+Alternatives
+------------
+
+N/A
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+wanghao<sxmatch1986@gmail.com>
+
+Milestones
+----------
+
+Rocky-3
+
+Work Items
+----------
+
+#* Change the Zaqar server code.
+#* Update API reference.
+#* Add release note for this feature.
+#* UTs for this feature.
+
+Dependencies
+============
+
+N/A