OFREP Single flag evaluation (Core API)

[emyller]

In order to implement the OFREP specification, our Core API needs a new endpoint that evaluates a single flag given a set of identity traits. The Edge API counterpart is Flagsmith/edge-api#712.

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

(request)

POST /ofrep/v1/evaluate/flags/{feature.name} HTTP/1.1
Host: {flagsmith_host}
X-API-Key: {server_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

{
  "key": "{feature.name}",
  "value": "{multivariate_feature_option.value}",
  "reason": "SPLIT",
  "variant": "{multivariate_feature_option.key}"
}

(response, unknown flag)

HTTP/1.1 404 Not Found
Content-Type: application/json

{
  "key": "{feature.name}",
  "errorCode": "FLAG_NOT_FOUND"
}

Acceptance criteria

• Our API exposes a new endpoint POST /ofrep/v1/evaluate/flags/{flagKey} compliant to the OFREP specification. As such, the endpoint:
  • Serves the flag's value as its remote configuration value, falling back to the flag's enabled state when no value is set.
  • Reports the flag's evaluation reason using the vocabulary OFREP defines.
  • Responds 404 Not Found when the environment has no such flag.
  • Is billed similarly to other billed endpoints.
  • Persists the identity and its traits on the same terms as identity flag evaluation.