Not possible to override headers in environment config

Q	A
Symfony version	v3.4.8
Bundle version	v7.4.0

I'm having issues to override options->headers in environment configurations. I have in config.yml the default configuration which should apply for all envs besides production. (especially important as I have the auth key in the headers)

Unfortunately its using still the config.yaml configuration instead of the one from config_production.yml.

When checking with debug:config I found out that the keys are just added as numerics instead of by their actual key. E.g. I added foobar: "test" in the headers section in staging and I'm getting the following output:

eight_points_guzzle:
    slow_response_time: 1000
    clients:
        abc:
            ...
            options:
                headers:
                    Accept: application/json
                    content-type: application/json
                    x-auth-token: abcdef
                    0: test

while it should show

eight_points_guzzle:
    slow_response_time: 1000
    clients:
        abc:
            ...
            options:
                headers:
                    Accept: application/json
                    content-type: application/json
                    x-auth-token: abcdef
                    foobar: test

I found a similar issue reported in https://github.com/symfony/symfony/issues/18988 where the proposed fix was to use useAttributeAsKey in the treebuilder. Any other ideas or options to achieve to add or override of headers in an environment config?

thanks in advance!

8p / EightPointsGuzzleBundle

Not possible to override headers in environment config #247