refactor(auth): Implement new initializer function API (#3012)

.changeset/perfect-lobsters-kiss.md

@@ -0,0 +1,38 @@
+---
+'@urql/exchange-auth': major
+---
+
+Implement new `authExchange` API, which removes the need for an `authState` (i.e. an internal authentication state) and removes `getAuth`, replacing it with a separate `refreshAuth` flow.
+
+The new API requires you to now pass an initializer function. This function receives a `utils`
+object with `utils.mutate` and `utils.appendHeaders` utility methods.
+It must return the configuration object, wrapped in a promise, and this configuration is similar to
+what we had before, if you're migrating to this. Its `refreshAuth` method is now only called after
+authentication errors occur and not on initialization. Instead, it's now recommended that you write
+your initialization logic in-line.
+
+```js
+authExchange(async utils => {
+  let token = localStorage.getItem('token');
+  let refreshToken = localStorage.getItem('refreshToken');
+  return {
+    addAuthToOperation(operation) {
+      return utils.appendHeaders(operation, {
+        Authorization: `Bearer ${token}`,
+      });
+    },
+    didAuthError(error) {
+      return error.graphQLErrors.some(e => e.extensions?.code === 'FORBIDDEN');
+    },
+    async refreshAuth() {
+      const result = await utils.mutate(REFRESH, { token });
+      if (result.data?.refreshLogin) {
+        token = result.data.refreshLogin.token;
+        refreshToken = result.data.refreshLogin.refreshToken;
+        localStorage.setItem('token', token);
+        localStorage.setItem('refreshToken', refreshToken);
+      }
+    },
+  };
+});
+```