doom

After a careful read of man curl, it appears that this might actually be the best way:
curl -K curlconfig.cfg http://www.googles

Then you insert this line to curlconfig.cfg (or what ever filename you like):
user = "defn:password"

Works like a charm. Also, you can add other curl options to that file as well as separate lines.

Thank you for these tips!
The reason the example with cat is not working as it is, is that cat prints out a newline from the file.
By removing the newline, the code will work:
{ echo -n 'user = "'; cat password.txt | tr -d '\n'; echo '"'; }
tr -d '\n' deletes the newline from the (end of the) data.