Ignore unchecked JWT claims

Previously, if a JWT claim was present, it was validated regardless of
whether it was required.

However, according to the spec [1]:

"all claims that are not understood by implementations MUST be ignored"

which we interpret to mean that we should not attempt to validate
claims we don't require.

With this change, only claims listed in required checks are validated.

[1] https://tools.ietf.org/html/rfc7519#section-4

1 files changed, 26 insertions, 10 deletions

diff --git a/src/jwtf/src/jwtf.erl b/src/jwtf/src/jwtf.erl
index 247f2b508..a0bbf1fc1 100644
--- a/src/jwtf/src/jwtf.erl
+++ b/src/jwtf/src/jwtf.erl
@@ -188,8 +188,7 @@ validate_alg(Props, Checks) ->
     end.
 
 
-%% Not all these fields have to be present, but if they _are_ present
-%% they must be valid.
+%% Only validate required checks.
 validate_payload(Props, Checks) ->
     validate_iss(Props, Checks),
     validate_iat(Props, Checks),
@@ -202,7 +201,7 @@ validate_iss(Props, Checks) ->
     ActualISS = prop(<<"iss">>, Props),
 
     case {ExpectedISS, ActualISS} of
-        {undefined, undefined} ->
+        {undefined, _} -> % ignore unrequired check
             ok;
         {ISS, undefined} when ISS /= undefined ->
             throw({bad_request, <<"Missing iss claim">>});
@@ -218,11 +217,11 @@ validate_iat(Props, Checks) ->
     IAT = prop(<<"iat">>, Props),
 
     case {Required, IAT} of
-        {undefined, undefined} ->
+        {undefined, _} -> % ignore unrequired check
             ok;
         {true, undefined} ->
             throw({bad_request, <<"Missing iat claim">>});
-        {_, IAT} when is_integer(IAT) ->
+        {true, IAT} when is_integer(IAT) ->
             ok;
         {true, _} ->
             throw({bad_request, <<"Invalid iat claim">>})
@@ -234,12 +233,12 @@ validate_nbf(Props, Checks) ->
     NBF = prop(<<"nbf">>, Props),
 
     case {Required, NBF} of
-        {undefined, undefined} ->
+        {undefined, _} -> % ignore unrequired check
             ok;
         {true, undefined} ->
             throw({bad_request, <<"Missing nbf claim">>});
-        {_, IAT} ->
-            assert_past(<<"nbf">>, IAT)
+        {true, NBF} ->
+            assert_past(<<"nbf">>, NBF)
     end.
 
 
@@ -248,11 +247,11 @@ validate_exp(Props, Checks) ->
     EXP = prop(<<"exp">>, Props),
 
     case {Required, EXP} of
-        {undefined, undefined} ->
+        {undefined, _} -> % ignore unrequired check
             ok;
         {true, undefined} ->
             throw({bad_request, <<"Missing exp claim">>});
-        {_, EXP} ->
+        {true, EXP} ->
             assert_future(<<"exp">>, EXP)
     end.
 
@@ -351,3 +350,20 @@ now_seconds() ->
 
 prop(Prop, Props) ->
     proplists:get_value(Prop, Props).
+
+
+-ifdef(TEST).
+-include_lib("eunit/include/eunit.hrl").
+
+validate_payload_ignore_unchecked_props_test() ->
+    ?assertEqual(ok, validate_payload(_Props = [], _Checks = [])),
+    BogusProps = [
+        {iss, bogus},
+        {iat, bogus},
+        {nbf, bogus},
+        {exp, bogus}
+    ],
+    ?assertEqual(ok, validate_payload(BogusProps, _Checks = [])),
+    ok.
+
+-endif.