Added server API description

api.txt

@@ -1,3 +1,5 @@
+Client API
+----------
 Basically the Authen::SASL module gathers some info. When ->client_new
 is called the plugin is called to create a $conn object. At that point
 it should query the Authen::SASL object for mechanisms and callbacks
@@ -7,7 +9,8 @@ Properties are then set on the $conn object by calling $conn->property
 Then client_start is called
 
 Then we call client_step with a challenge string to get a response
-string.
+string. need_step can be called to check that this step is actually
+necessary for the selected mechanism.
 
 
 Quite simple really I think.
@@ -18,12 +21,37 @@ So the plugin just needs to support
   client_new
   client_start
   client_step
+  need_step    # returns true if client_step needs to be called
   property     # set/get for properties
   mechanism    # returns the name of the chosen mechanism
   service      # the service name passed to client_new
   host         # the hostname passed to client_new
+  is_success   # returns true if authentication suceeded
 
+Server API
+----------
+The server API is symetric to the client's one. server_new is called to
+create a connection object. Then server_start is called, and if relevant
+the first data from the client is passed to it as argument.
 
+Then we call server_step with all the response from the clients, which
+returns challenges. need_step also determines if the current mechanism
+requires another step.
+
+So the plugin just needs to support
+
+  server_new
+  server_start
+  server_step
+  need_step    # returns true if client_step needs to be called
+  property     # set/get for properties
+  mechanism    # returns the name of the chosen mechanism
+  service      # the service name passed to client_new
+  host         # the hostname passed to client_new
+  is_success   # returns true if authentication suceeded
+
+Callbacks
+---------
 properties and callbacks are passed by name, so you will need to convert
 them to numbers.