Issue using COPY command with AWS Redshift
Perhaps the JSON you have is not quite correct. When I paste your JSON into jsonlint.com I get the following:

Parse error on line 7: 
...        "username": “user23"} ] }
-----------------------^
Expecting 'STRING', 'NUMBER', 'NULL', 'TRUE', 'FALSE', '{', '['


The AWS Redshift documentation on COPY SSH parameters has the following 


  The quote characters must be simple quotation marks (0x22), not slanted or "smart" quotation marks. 


So double check you quote marks around the username you've provided, and if they are how you've provided them above, change it from to “user23" >> "user23" (note the first quote mark is different).


The first quote mark in your code is unicode : U+201C and not U+0022