Added way to send requests to forward proxy for enabled customer and data sources

[bhuvan-teja-glean]

Description:
Currently our glean-proxy will make a direct connection to a data source. We want to provide a way to route these requests via forward proxy. So that the requests can be monitored by the forward proxy.

We need to set the following environment variables to make the requests go through the forward proxy:

export FORWARD_PROXY_HOST=<forward-proxy-host>
export FORWARD_PROXY_PORT=<forward-proxy-port>
export FORWARD_PROXY_DATA_SOURCE_HOSTS=<Comma seperated list of data source hosts>
export FORWARD_PROXY_USERNAME=<Username of the forward proxy>
export FORWARD_PROXY_PASSWORD=<Password of the forward proxy>

Context:

We needed this so that the customer can host a forward proxy which can inspect all the requests going to the data sources.

Test plan:
Ran the glean-proxy server with the following environment variable
bazel run //src/main/java/com/glean/proxy:ProxyMain 8080
Environment variables

export CLOUD_PLATFORM=AWS
export AWS_FILTERS=
export GOOGLE_FILTERS=
export CROSS_PLATFORM_FILTERS=
export DEBUG_FILTERS=
export FORWARD_PROXY_HOST=localhost
export FORWARD_PROXY_PORT=8888
export FORWARD_PROXY_DATA_SOURCE_HOSTS=www.google.com,www.glean.com
export FORWARD_PROXY_USERNAME=
export FORWARD_PROXY_PASSWORD=

For the forward proxy we just used the glean-proxy to run as forward proxy with a different port
bazel run //src/main/java/com/glean/proxy:ProxyMain 8888
Environment variables

export CLOUD_PLATFORM=AWS
export AWS_FILTERS=
export GOOGLE_FILTERS=
export CROSS_PLATFORM_FILTERS=
export DEBUG_FILTERS=

Made the following requests

1. curl --proxy localhost:8080 https://www.example.com
2. curl --proxy localhost:8080 https://www.google.com

Screenshot of glean-proxy at 8080 logs

Screenshot of forward-proxy at 8888 logs

As you see only www.google.com went through the forward proxy and www.example.com doesn't have any log in the forward proxy as it is a direct connection

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Change Type

• Flag-gated development/Internal fix
• Bug Fix/Enhancement
• Security or Permissions related change
• Feature launch

Platform (Choose one if applicable)

• AWS only change
• GCP only change