Update client header values.

[kuderdev]

I think it is already fixed. We only add default parameters if there is no parameter with the same name available in the list of request parameters. It can be overridden by AllowMultipleDefaultParametersWithSameName, which is false by default.

Originally posted by @alexeyzimarev in #959 (comment)

I am not sure this solves the problem. If we set this to true wouldn't that mean he would have multiple headers with the same name and different tokens?

We need a AddOrUpdate like parameters has.

[Lramelot]

Created the PR #1576 to fix this issue :)