OFREP Bulk flag evaluation (Core API)

[emyller]

In order to implement the OFREP specification, our Core API needs a new endpoint that evaluates all flags in an environment given a set of identity traits. The Edge API counterpart is Flagsmith/edge-api#711.

An interpretation of the specification to our data model is as the following example:

(request)

POST /ofrep/v1/evaluate/flags HTTP/1.1
Host: {flagsmith_host}
X-API-Key: {client_side_environment_key}
Content-Type: application/json

{
  "context": {
    "targetingKey": "{identity.identifier}",
    "trait1": "value1",
    "trait2": "value2"
  }
}

(response)

HTTP/1.1 200 OK
Content-Type: application/json
ETag: "{etag}"

{
  "flags": [
    {
      "key": "{feature.name}",
      "value": "{feature_state.feature_state_value}",
      "reason": "TARGETING_MATCH"
    },
    {
      "key": "{feature.name}",
      "value": {feature_state.enabled},
      "reason": "STATIC"
    },
    {
      "key": "{feature.name}",
      "value": "{multivariate_feature_option.value}",
      "reason": "SPLIT",
      "variant": "{multivariate_feature_option.key}"
    }
  ],
  "metadata": {
    "version": "{environment.updated_at}"
  }
}

Acceptance criteria

• Our API exposes a new endpoint POST /ofrep/v1/evaluate/flags compliant to the OFREP specification. As such, the endpoint:
  • Responds with an ETag header derived from the response body.
  • Accepts an If-None-Match header which can lead to a 304 Not Modified response.
  • Serves each flag's value as its remote configuration value, falling back to the flag's enabled state when no value is set.
  • Reports each flag's evaluation reason using the vocabulary OFREP defines.
  • Is billed similarly to other billed endpoints.
  • Persists the identity and its traits on the same terms as identity flag evaluation.

Important

Server-Sent Events stream lookups are out of scope for this issue.