How to authenticate on 2 different symfony2 firewalls at the same time?

Question

I have a Symfony application with 2 areas, one for clients accessing from a web page an other for API calls from AJAX and web services.

Each one of this areas is protected with a firewall on its own. The WEB interface is authenticated with a log in form and the API with http_basic.

Both firewalls work fine, but when the WEB interface makes an AJAX call to the API interface, then the browser prompts the user to log in again, even when he was already logged in (via log in form). This is what I want to avoid. I Would like that both firewalls were authenticated at the same time to prevent this prompt.

I've seen another question with exactly the same problem. But they are using http_basic authentication on both firewalls, so, the solution proposed did't work on my case:

Authenticate multiple symfony2 firewalls with one login form

My security.yml

#....
firewalls:
    api:
        pattern:    ^/API
        context: primary_auth
        stateless:  true
        http_basic: 
            realm: "API: Please log in"

    web:
        pattern:    ^/
        context: primary_auth
        form_login:
            check_path: /login_check
            login_path: /login
            provider: fos_userbundle
        logout:
            path:   /logout
            target: /
        anonymous: ~

Answer 1

You might want to look here: Authenticate multiple symfony2 firewalls with one login form there's solution to similar problem there

quoted:

security:
# providers etc ...

    firewall:
        main:
            pattern: # ...
            provider: my_users
            http_basic: ~
            context: primary_auth  # new
        api:
            pattern: # ...
            provider: my_users
            http_basic: ~
            context: primary_auth  # new