Implement decoding of CBOR major_type_value=2 additional_type_value=25

This use case came up when testing a long email as username,
which made the authData exceed 256 bytes.

Also add a webauthn.raise_error() helper-function to raise an error
if we run into a CBOR type which we currently can't decode.

Author: joelonsql

FUNCTIONS/decode_cbor.sql

@@ -37,6 +37,8 @@ WITH RECURSIVE x AS (
          THEN substring(x.cbor,2,additional_type_value)
          WHEN major_type_value = 2 AND additional_type_value = 24
          THEN substring(x.cbor,3,get_byte(x.cbor,1))
+         WHEN major_type_value = 2 AND additional_type_value = 25
+         THEN substring(x.cbor,4,get_byte(x.cbor,1)*256+get_byte(x.cbor,2))
     END AS bytes,
     CASE WHEN major_type_value = 0 AND additional_type_value <= 23
          THEN additional_type_value
@@ -50,10 +52,16 @@ WITH RECURSIVE x AS (
   )) AS data_item_header(major_type_value,additional_type_value) ON TRUE
   JOIN LATERAL (VALUES(CASE
     WHEN major_type_value IN (2,3) AND additional_type_value <= 23 THEN 2+additional_type_value
-    WHEN major_type_value = 5 THEN 2
+    WHEN major_type_value = 5 AND additional_type_value <= 23 THEN 2
     WHEN major_type_value = 2 AND additional_type_value = 24 THEN 3+get_byte(x.cbor,1)
+    WHEN major_type_value = 2 AND additional_type_value = 25 THEN 4+get_byte(x.cbor,1)*256+get_byte(x.cbor,2)
     WHEN major_type_value = 0 AND additional_type_value <= 23 THEN 2
     WHEN major_type_value = 1 AND additional_type_value <= 23 THEN 2
+    ELSE webauthn.raise_error('Decoding of CBOR type not implemented',json_build_object(
+      'item',item,
+      'major_type_value',major_type_value,
+      'additional_type_value',additional_type_value
+    ),NULL::integer)
   END)) AS next_item(byte_offset) ON TRUE
   WHERE length(x.cbor) > 0
 )

FUNCTIONS/raise_error.sql

@@ -0,0 +1,12 @@
+CREATE OR REPLACE FUNCTION webauthn.raise_error(error_message text, debug json, dummy_return_value anyelement)
+RETURNS anyelement
+LANGUAGE plpgsql
+AS $$
+BEGIN
+RAISE '% %', error_message, debug;
+-- Will not return, since error will be raised,
+-- but necessary to be able to use the function in place
+-- where a value of given type is expected.
+RETURN dummy_return_value;
+END;
+$$;

Makefile

@@ -23,6 +23,7 @@ all: webauthn--1.0.sql
 
 SQL_SRC = \
   complain_header.sql \
+	FUNCTIONS/raise_error.sql \
 	ENUMS/credential_type.sql \
 	ENUMS/user_verification_requirement.sql \
   FUNCTIONS/base64url_decode.sql \