feat: set TF_APPEND_USER_AGENT environment variable

[lyoung-confluent]

what

Many Terraform providers will respect the TF_APPEND_USER_AGENT environment variable and append it to the existing provider/terraform user-agent when making HTTP requests.

This change sets the value to indicate that Terraform is running within Atlantis and includes the PR URL, head commit SHA and username who triggered the command (NOTE: this is not necessarily the PR author). It is set before custom environment variables so users who have set this manually (ex: #2651) will still have their own value set.

why

It's useful to have this information in logs (ex: CloudTrail) to identify exactly what PR modified a resource.

tests

I added a test for this new variable.

references

• Previous PR closed due to inactivity: feat: Add TF_APPEND_USER_AGENT to environment variables #2688
• Closes Docs on appending the user agent with relevant atlantis information #2651

[lyoung-confluent]

@nitrocode Any other feedback/concerns on this PR? I'd like to get it merged/address any feedback before it gets eaten by the stale PR robot again like #2688 was 😄

[nitrocode]

Thanks @lyoung-confluent for the changes. I added a couple comments

[lyoung-confluent]

@nitrocode I finally got a chance to test this, it does NOT work. The environment variable gets set for custom workflows without issue, but a default plan/apply steps do not work, it seems only these environment variables are set for the executed terraform process:

atlantis/server/core/terraform/tfclient/terraform_client.go

Lines 432 to 437 in 315e25b

	// Will de-emphasize specific commands to run in output.
	"TF_IN_AUTOMATION=true",
	// Cache plugins so terraform init runs faster.
	fmt.Sprintf("WORKSPACE=%s", workspace),
	fmt.Sprintf("ATLANTIS_TERRAFORM_VERSION=%s", v.String()),
	fmt.Sprintf("DIR=%s", path),

I'm curious what you would suggest as a fix, it seems that I would have to inject the values somewhere around here for it to be present consistently?

atlantis/server/events/project_command_runner.go

Lines 827 to 834 in 315e25b

	case "env":
	out, err = p.EnvStepRunner.Run(ctx, step.RunShell, step.RunCommand, step.EnvVarValue, absPath, envs)
	envs[step.EnvVarName] = out
	// We reset out to the empty string because we don't want it to
	// be printed to the PR, it's solely to set the environment variable.
	out = ""
	case "multienv":
	out, err = p.MultiEnvStepRunner.Run(ctx, step.RunShell, step.RunCommand, absPath, envs, step.Output)

[lyoung-confluent]

Okay, so this diff works (verified using local instance), only problem now is it's not being actually exercised in a test...