[exporter/signalfxexporter] allow user to add their own CA to the cert pool

[dloucasfx]

Signed-off-by: Dani Louca dlouca@splunk.com

Description:
Adding new feature to allow the user to add their own CA to the ingest and api client cert pool.
This is needed when the exporter is pointing to a TLS enabled signalfx receiver or/and TLS enabled http_forwarder
and the CA is not in the system cert pool (ex: agent <--> GW setup)

Testing:
Unit test and manual validation

Documentation:

ingest_ca_file and api_url can be used to set the absolute path to the CA file.
This is needed when the exporter is pointing to a TLS enabled signalfx receiver or/and TLS enabled http_forwarder
and the CA is not in the system cert pool

[dmitryax]

Can we apply https://github.com/open-telemetry/opentelemetry-collector/blob/main/config/configtls/README.md instead?

[dloucasfx]

Can we apply https://github.com/open-telemetry/opentelemetry-collector/blob/main/config/configtls/README.md instead?

yes, I can make that change.
One thing reading the configtls code, if I ended up using LoadTLSConfig the code will not append the CA cert to the system cert pool, I guess this is fine as the client is only used to talk to this one endpoint, do you see any other reasons that we might need the system certs?

[dmitryax]

few nits, otherwise LGTM

[dmitryax]

@dloucasfx please take a look at the failing tests

[dloucasfx]

@dloucasfx please take a look at the failing tests

It's a difference in error message between golang 1.19 (the version I developed with) and 1.18 where the CI is failing.

1.18 error:

error making HTTP request to https://127.0.0.1:45393/v2/dimension/key/id/_/sfxagent: Patch \"https://127.0.0.1:45393/v2/dimension/key/id/_/sfxagent\": x509: certificate signed by unknown authority

1.19 error:

error making HTTP request to https://127.0.0.1:65128/v2/dimension/key/id/_/sfxagent: Patch "https://127.0.0.1:65128/v2/dimension/key/id/_/sfxagent": x509: “OpenTelemetry Collector” certificate is not trusted

I used regex instead of contains and this error making HTTP request.*x509 should work fine on both... test updated.

[codeboten]

Looks like github-action re-requested a review from you @dmitryax, can you confirm this is still good? I'm not sure what triggered the action after your approval 🤔

[dmitryax]

Maybe because of additional commits after that. It's good to merge