Hello,
http://wiki.nginx.org/HttpLuaModule#ngx.location.capture
res.header holds all the response headers of the subrequest and it is a normal Lua table. For multi-value response headers, the value is a Lua (array) table that holds all the values in the order that they appear. For instance, if the subrequest response headers contain the following lines:
Set-Cookie: a=3
Set-Cookie: foo=bar
Set-Cookie: baz=blah
Then res.header["Set-Cookie"] will be evaluated to the table value {"a=3", "foo=bar", "baz=blah"}.