Step 1
POST a JSON object with your search terms:
$ curl -s -f -H "Content-Type: application/json" -X POST \
"https://dspacetest.cgiar.org/rest/items/find-by-metadata-field?expand=bitstreams" \
-d '{"key":"dcterms.subject", "value":"climate variability","language": "en_US"}' | \
python -m json.tool
...