Add equivalent test for #681

the v2 branch seems to have received fixes during the refactoring,
and symptoms described in #681 did not show up. However, out of
caution we will add this test that checks for #681 so that future
regressions may be prevented

jws/jws_test.go

@@ -1814,3 +1814,22 @@ func TestAlgorithmsForKey(t *testing.T) {
 		})
 	}
 }
+
+func TestGH681(t *testing.T) {
+	privkey, err := jwxtest.GenerateRsaKey()
+	if !assert.NoError(t, err, "failed to create private key") {
+		return
+	}
+
+	buf, err := jws.Sign(nil, jws.WithKey(jwa.RS256, privkey), jws.WithDetachedPayload([]byte("Lorem ipsum")))
+	if !assert.NoError(t, err, "failed to sign payload") {
+		return
+	}
+
+	t.Logf("%s", buf)
+
+	_, err = jws.Verify(buf, jws.WithKey(jwa.RS256, &privkey.PublicKey), jws.WithDetachedPayload([]byte("Lorem ipsum")))
+	if !assert.NoError(t, err, "failed to verify JWS message") {
+		return
+	}
+}