Implement Labrinth Canary API flag (#5531)

apps/frontend/src/composables/fetch.js

@@ -5,6 +5,7 @@
 
 let cachedRateLimitKey = undefined
 let rateLimitKeyPromise = undefined
+const LABRINTH_CANARY_COOKIE = 'labrinth-canary=always'
 
 async function getRateLimitKey(config) {
 	if (config.rateLimitKey) return config.rateLimitKey
@@ -38,6 +39,15 @@ export const useBaseFetch = async (url, options = {}, skipAuth = false) => {
 		options.headers['x-ratelimit-key'] = await getRateLimitKey(config)
 	}
 
+	if (useFeatureFlags().value.labrinthApiCanary) {
+		const existingCookie = options.headers.cookie
+		if (!existingCookie?.split('; ').includes(LABRINTH_CANARY_COOKIE)) {
+			options.headers.cookie = existingCookie
+				? `${existingCookie}; ${LABRINTH_CANARY_COOKIE}`
+				: LABRINTH_CANARY_COOKIE
+		}
+	}
+
 	if (!skipAuth) {
 		const auth = await useAuth()