docs: Add documentation about contrib/sim-rest-{server,client}

Those programs have been around since 2021 but we never had any
documentation here. Let's fix that.

Change-Id: I7c471cac9500db063a0c8f5c5eb7b6861b3234ed

docs/index.rst

@@ -43,6 +43,7 @@ pySim consists of several parts:
    legacy
    library
    osmo-smdpp
+   sim-rest
 
 
 Indices and tables

docs/sim-rest.rst

@@ -0,0 +1,118 @@
+sim-rest-server
+===============
+
+Sometimes there are use cases where a [remote] application will need
+access to a USIM for authentication purposes.  This is, for example, in
+case an IMS test client needs to perform USIM based authentication
+against an IMS core.
+
+The pysim repository contains two programs: `sim-rest-server.py` and
+`sim-rest-client.py` that implement a simple approach to achieve the
+above:
+
+`sim-rest-server.py` speaks to a [usually local] USIM via the PC/SC
+API and provides a high-level REST API towards [local or remote]
+applications that wish to perform UMTS AKA using the USIM.
+
+`sim-rest-client.py` implements a small example client program to
+illustrate how the REST API provided by `sim-rest-server.py` can be
+used.
+
+REST API Calls
+--------------
+
+POST /sim-auth-api/v1/slot/SLOT_NR
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+where SLOT_NR is the integer-encoded slot number (corresponds to PC/SC
+reader number).  When using a single sysmoOCTSIM board, this is in the range of 0..7
+
+Example: `/sim-auth-api/v1/slot/0` for the first slot.
+
+Request Body
+############
+
+The request body is a JSON document, comprising of
+    1. the RAND and AUTN parameters as hex-encoded string
+    2. the application against which to authenticate (USIM, ISIM)
+
+Example:
+::
+
+        {
+            "rand": "bb685a4b2fc4d697b9d6a129dd09a091",
+            "autn": "eea7906f8210000004faf4a7df279b56"
+        }
+
+HTTP Status Codes
+#################
+
+HTTP status codes are used to represent errors within the REST server
+and the SIM reader hardware.  They are not used to communicate protocol
+level errors reported by the SIM Card.  An unsuccessful authentication
+will hence have a `200 OK` HTTP Status code and then encode the SIM
+specific error information in the Response Body.
+
+======  =========== ================================
+Status  Code        Description
+------  ----------- --------------------------------
+200     OK          Successful execution
+400     Bad Request Request body is malformed
+404     Not Found   Specified SIM Slot doesn't exist
+410     Gone        No SIM card inserted in slot
+======  =========== ================================
+
+Response Body
+#############
+
+The response body is a JSON document, either
+
+#. a successful outcome; encoding RES, CK, IK as hex-encoded string
+#. a sync failure; encoding AUTS as hex-encoded string
+#. errors
+   #. authentication error (incorrect MAC)
+   #. authentication error (security context not supported)
+   #. key freshness failure
+   #. unspecified card error
+
+Example (succcess):
+::
+
+        {
+           "successful_3g_authentication": {
+                "res": "b15379540ec93985",
+                "ck": "713fde72c28cbd282a4cd4565f3d6381",
+                "ik": "2e641727c95781f1020d319a0594f31a",
+                "kc": "771a2c995172ac42"
+            }
+        }
+
+Example (re-sync case):
+::
+
+        {
+            "synchronisation_failure": {
+                "auts": "dc2a591fe072c92d7c46ecfe97e5"
+            }
+        }
+
+Concrete example using the included sysmoISIM-SJA2
+--------------------------------------------------
+
+This was tested using SIMs ending in IMSI numbers 45890...45899
+
+The following command were executed successfully:
+
+Slot 0
+::
+
+        $ /usr/local/src/pysim/contrib/sim-rest-client.py -c 1 -n 0 -k 841EAD87BC9D974ECA1C167409357601 -o 3211CACDD64F51C3FD3013ECD9A582A0
+        -> {'rand': 'fb195c7873b20affa278887920b9dd57', 'autn': 'd420895a6aa2000089cd016f8d8ae67c'}
+        <- {'successful_3g_authentication': {'res': '131004db2ff1ce8e', 'ck': 'd42eb5aa085307903271b2422b698bad', 'ik': '485f81e6fd957fe3cad374adf12fe1ca', 'kc': '64d3f2a32f801214'}}
+
+Slot 1
+::
+
+        $ /usr/local/src/pysim/contrib/sim-rest-client.py -c 1 -n 1 -k 5C2CE9633FF9B502B519A4EACD16D9DF -o 9834D619E71A02CD76F00CC7AA34FB32
+        -> {'rand': '433dc5553db95588f1d8b93870930b66', 'autn': '126bafdcbe9e00000026a208da61075d'}
+        <- {'successful_3g_authentication': {'res': '026d7ac42d379207', 'ck': '83a90ba331f47a95c27a550b174c4a1f', 'ik': '31e1d10329ffaf0ca1684a1bf0b0a14a', 'kc': 'd15ac5b0fff73ecc'}}