Flow: add OpenTelemetry Collector extension components

[rfratto]

This issue extends #2213 and proposes a set of otelcol components which wrap around OpenTelemetry Collector extensions.

Background

#2343 added the otelcol.exporter.otlp component, wrapping around the OpenTelemetry Collector otlp exporter. The upstream exporter can be configured with a reference to an ID of an extension component to use for authentication. The instance of the component is then retrieved from the component.Host instance.

Authentication was descoped from the initial PR while an approach to handle extensions was undetermined.

There were two approaches that could be taken:

1. Bake in support for authentication into components, similar to what is done for the prometheus.remote_write component.
2. Introduce new components which handle authentication extensions and allow the user to wire them together.

To remain close to how upstream handles it, this issue proposes the latter approach.

Proposal

We will create a set of OpenTelemetry Collector extension components in an otelcol.auth namespace. The namespace will be composed of OpenTelemetry Collector extensions which are intended for authentication and implement one or more of the interfaces from the OpenTelemetry Collector configauth package.

Other extensions are considered out of scope for this proposal. Storage extensions are likely to be included eventually, but are out of scope due to being experimental. Extensions that aren't authentication extensions or storage extensions may be added in the future, but would likely belong in a dedicated namespace rather than being scoped to otelcol.

Exported fields

otelcol.auth namespace will support the following exported fields:

• handler: The raw OpenTelemetry Collector extension instance which other components can use.

Example config

otelcol.exporter.otlp "default" {
  // Configure this component to use otelcol.auth.basic.default 
  // for authentication. 
  auth = otelcol.auth.basic.default.handler 

  ...
}

otelcol.auth.basic "default" {
  username = ...
  password = ... 
}

Flow component list

We will cherry-pick specific OpenTelemetry Collector extensions from both the otelcol and otelcol-contrib distributions to include in Grafana Agent Flow. Our initial set of extensions is minimal, but will grow over time.

We will start with the following extensions:

otelcol-contrib distribution components:

• otelcol.auth.basic: Performs Basic authentication (from basicauthextension).
• otelcol.auth.bearer: Performs Bearer token authentication (from bearertokenauthextension).
• otelcol.auth.headers: Adds custom headers for authentication (from headerssetterextension).
• otelcol.auth.oauth2: Performs OAuth2 authentication (from oauth2clientauthextension).
• otelcol.auth.sigv4: Performs SigV4 authentication (from sigv4authextension).

Tasks

This is the list of components to implement for the initial set of extensions:

• Flow: otelcol.auth.basic component #2354
• Flow: otelcol.auth.bearer component #2355
• Flow: otelcol.auth.headers component #2356
• Flow: otelcol.auth.oauth2 component #2357
• Flow: otelcol.auth.sigv4 component #2358

[fawadasaurus]

I can't wait for headerssetterextension support. I switched to Otel collector because of it. It will be nice to have the choice to switch back to Grafana Agent once that is available.

[rfratto]

This is completed; all tracking tasks are done.