gistfile1.txt

Request body: 
{"parameters":[{"name":"text","type":"secure-string","scope":"local","value":{"secure-string":{"value":"test"}}}]}
Response:
HTTP/1.1 400 1 error(s) found: [ { text - Error getting attribute value : SecureString too short or bad encoding ! } ]

I did several tests before posting this as a tweet reply (accidentally using @vcoteam acct instead of my own)... Not sure why the inner value is "string" instead of also being "SecureString" but both datatypes are compatible and this seems to work:

{"parameters":[{"name":"text","type":"SecureString","scope":"local","value":{"string":{"value":"test"}}}]}