Client-Side OFREP Provider

This provider is designed to use the OpenFeature Remote Evaluation Protocol (OFREP).

Installation

npm

npm install @openfeature/ofrep-web-provider

yarn

yarn add @openfeature/ofrep-web-provider @openfeature/ofrep-core @openfeature/web-sdk @openfeature/core

[!NOTE] yarn requires manual installation of peer dependencies

Configurations and Usage

The provider needs the base url of the OFREP server for instantiation.

import { OFREPWebProvider } from '@openfeature/ofrep-web-provider';

OpenFeature.setProvider(new OFREPWebProvider({ baseUrl: 'https://localhost:8080' }));

Polling and refresh

By default, polling is disabled (pollInterval defaults to 0). To enable periodic flag re-evaluation, set pollInterval to a positive number of milliseconds:

OpenFeature.setProvider(new OFREPWebProvider({ baseUrl: 'https://localhost:8080', pollInterval: 60_000 }));

Flags are automatically re-fetched when the page becomes visible (e.g. the user switches back to the tab). This follows ADR-0010 and is enabled by default. To opt out:

OpenFeature.setProvider(new OFREPWebProvider({ baseUrl: 'https://localhost:8080', disableVisibilityRefresh: true }));

HTTP headers

The provider can use headers from either a static header map or a custom header factory.

Static Headers

Headers can be given as a list of tuples or as a map of headers.

import { OFREPWebProvider } from '@openfeature/ofrep-web-provider';

OpenFeature.setProvider(
  new OFREPWebProvider({
    baseUrl: 'https://localhost:8080',
    headers: [
      ['Authorization', `my-api-key`],
      ['X-My-Header', `CustomHeaderValue`],
    ],
  }),
);

import { OFREPWebProvider } from '@openfeature/ofrep-web-provider';

OpenFeature.setProvider(
  new OFREPWebProvider({
    baseUrl: 'https://localhost:8080',
    headers: { Authorization: `my-api-key`, 'X-My-Header': `CustomHeaderValue` },
  }),
);

Header Factory

The header factory is evaluated before every flag evaluation which makes it possible to use dynamic values for the headers.

The following shows an example of loading a token and using it as bearer token.

import { OFREPWebProvider } from '@openfeature/ofrep-web-provider';

OpenFeature.setProvider(
  new OFREPWebProvider({
    baseUrl: 'https://localhost:8080',
    headersFactory: () => {
      const token: string = loadDynamicToken();
      return [['Authorization', `Bearer ${token}`]];
    },
  }),
);

Caching

The provider supports persistent local caching via localStorage per ADR-0009. Caching reduces latency on startup and improves resilience to transient network failures.

Cache modes

cacheMode controls the startup strategy:

• 'local-cache-first' (default) — initialize() resolves immediately from the persisted cache if one exists, then refreshes from the network in the background. Evaluations served before the refresh completes will have reason CACHED.
• 'network-first' — initialize() blocks on the network request. The persisted cache is used as a fallback only on transient failures (network unavailable, timeout, 5xx). Auth and configuration errors (400, 401, 403, 404) are always surfaced immediately and never masked by cached values.
• 'disabled' — no persistence. initialize() always blocks on the network and the other cache options have no effect.

cacheTTL — maximum age in seconds of a persisted cache entry before it is treated as a miss and removed. Defaults to 2_592_000 (30 days). Auth and configuration errors do not clear persisted entries; TTL governs expiry.

Cache key

Persisted entries are keyed by a hash of key material returned by a cache-key generator, not the full evaluation context. The default generator uses:

1. baseUrl — the configured OFREP base URL
2. Auth credential — serialized from known auth headers (Authorization, Api-Key, X-Api-Key, X-Auth-Token, X-Access-Token), taken from headers and headersFactory at read/write time
3. domain — the OpenFeature domain the provider is bound to via OpenFeature.setProvider('domain', provider) (passed to initialize() by the SDK; empty when registered as the default provider)
4. targetingKey — the evaluation context's targeting key

Use cacheKeyGenerator to customize the key material (namespace instances, drop auth for rotating tokens, or include stable context fields). The provider always hashes whatever the generator returns.

Only omit input.auth when authentication cannot affect flag results for the same baseUrl, domain, and targetingKey. Otherwise retain input.auth or include another stable identity discriminator so different credentials do not share persisted values.

The localStorage key is ofrep-web-provider:v2:{hash} where {hash} is the first 16 hex characters of SHA-256 (or an FNV-1a fallback in non-secure contexts where crypto.subtle is unavailable).

Domain scoping

The provider declares itself domain-scoped, so each instance is bound to at most one OpenFeature domain via OpenFeature.setProvider('domain', provider). The SDK forwards that domain to initialize(context, domain?); persistence is not initialized until then, so nothing is read from or written to localStorage before initialization.

Bind a separate provider instance per domain in micro-frontend or multi-tenant setups:

OpenFeature.setProvider('billing', new OFREPWebProvider({ baseUrl: 'https://flags.example.com' }));
OpenFeature.setProvider('checkout', new OFREPWebProvider({ baseUrl: 'https://flags.example.com' }));

Auth headers and rotating tokens

Only the auth header names listed above participate in the cache key. Other custom headers (for example X-My-Header) are sent on requests but do not affect persistence.

import { OFREPWebProvider } from '@openfeature/ofrep-web-provider';

OpenFeature.setProvider(
  'my-app',
  new OFREPWebProvider({
    baseUrl: 'https://localhost:8080',
    cacheMode: 'local-cache-first',
    cacheTTL: 3600, // 1 hour
    cacheKeyGenerator: (input) => `my-app:${JSON.stringify([input.url, input.auth, input.domain, input.targetingKey])}`,
    headers: [['Authorization', 'my-api-key']],
  }),
);

Fetch implementation

If needed, a custom fetch implementation can be injected, if e.g. the platform does not have fetch built in.

import { OFREPWebProvider } from '@openfeature/ofrep-web-provider';
import { fetchPolyfill } from 'some-fetch-polyfill';

OpenFeature.setProvider(
  new OFREPWebProvider({
    baseUrl: 'https://localhost:8080',
    fetchImplementation: fetchPolyfill,
  }),
);

Building

Run nx package providers-ofrep-web to build the library.

Running unit tests

Run nx test providers-ofrep-web to execute the unit tests via Jest.