Improved proxy support via standard environment variables

[romain-grecourt]

Environment Details

• Helidon Version: 3.2.2

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Problem Description

Add general support for the standard http[s]_proxy and no_proxy environment variables:

• WebClient
• Everything else

E.g. Using google-login security provider, one has to do this:

security:
  providers:
    - google-login:
        proxy-host: "proxy.acme.com"
        proxy-port: "80"

Yes, this can be overridden with environment variables like this:

export security_providers_0_google_dash_login_proxy_dash_host="proxy.acme.com"
export security_providers_0_google_dash_login_proxy_dash_host="80"

However, this is cumbersome. Also. this configuration is provider specific, so adding another provider would make it worse.

Instead we should support the defacto standard *NIX user experience:

export http_proxy="proxy.acme.com:80"
export https_proxy="proxy.acme.com:80"
export no_proxy="localhost,127.0.0.1,*.acme.com"

# every integrated outbound call is configured
java -jar myapp.jar

It could be done with JAVA_TOOL_OPTIONS, but that makes one more variable to change when switch on and off proxy.
Supporting the standard environment variables simplifies the user experience.

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We should provide a generic mechanism in a common module to be used by any code that makes outbound calls (E.g. GoogleTokenProvider).

We could abstract io.helidon.webclient.Proxy to decouple it from WebClient and add the environment variable support.