fix: authz_keycloak plugin giving 500 error #1626

Job	Run time
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[a-k]*)	30m 4s
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[l-z]*)	30m 7s
run ci on redhat ubi (lua-resty-worker-events, t/admin t/cli t/config-center-yaml t/control t/cor...	21m 21s
run ci on redhat ubi (lua-resty-worker-events, t/node t/pubsub t/router t/script t/secret t/strea...	20m 36s
run ci on redhat ubi (lua-resty-events, t/plugin/[a-k]*)	29m 40s
run ci on redhat ubi (lua-resty-events, t/plugin/[l-z]*)	31m 36s
run ci on redhat ubi (lua-resty-events, t/admin t/cli t/config-center-yaml t/control t/core t/deb...	21m 24s
run ci on redhat ubi (lua-resty-events, t/node t/pubsub t/router t/script t/secret t/stream-node ...	21m 25s
	3h 26m 13s

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