fix(jwt): preserve client plugin inference with jwtClient (#10513)

Co-authored-by: Cursor <cursoragent@cursor.com>

.changeset/fix-jwt-client-plugin-inference.md

@@ -0,0 +1,5 @@
+---
+"better-auth": patch
+---
+
+Fix `jwtClient()` collapsing `createAuthClient` type inference when combined with other client plugins such as `inferAdditionalFields`. Additional user fields (for example on `updateUser`) are preserved again.

packages/better-auth/src/plugins/jwt/client.ts

@@ -1,4 +1,10 @@
-import type { BetterAuthClientPlugin } from "@better-auth/core";
+import type {
+	BetterAuthClientOptions,
+	BetterAuthClientPlugin,
+	ClientFetchOption,
+	ClientStore,
+} from "@better-auth/core";
+import type { BetterFetch } from "@better-fetch/fetch";
 import type { JSONWebKeySet } from "jose";
 import { PACKAGE_VERSION } from "../../version";
 import type { jwt } from "./index";
@@ -25,8 +31,12 @@ export const jwtClient = (options?: JwtClientOptions) => {
 		pathMethods: {
 			[jwksPath]: "GET",
 		},
-		getActions: ($fetch) => ({
-			jwks: async (fetchOptions?: any) => {
+		getActions: (
+			$fetch: BetterFetch,
+			_$store: ClientStore,
+			_options: BetterAuthClientOptions | undefined,
+		) => ({
+			jwks: async (fetchOptions?: ClientFetchOption) => {
 				return await $fetch<JSONWebKeySet>(jwksPath, {
 					method: "GET",
 					...fetchOptions,

packages/better-auth/src/plugins/jwt/jwt.test.ts

@@ -1,8 +1,10 @@
+import type { BetterAuthClientPlugin } from "@better-auth/core";
 import type { JSONWebKeySet } from "jose";
 import { createLocalJWKSet, jwtVerify } from "jose";
-import { describe, expect, it } from "vitest";
+import { describe, expect, expectTypeOf, it } from "vitest";
 import { createAuthClient } from "../../client";
 import { getTestInstance } from "../../test-utils/test-instance";
+import { inferAdditionalFields } from "../additional-fields/client";
 import { jwt } from ".";
 import { jwtClient } from "./client";
 import type { JWKOptions, Jwk, JwtOptions } from "./types";
@@ -833,3 +835,46 @@ describe("toExpJWT", () => {
 		});
 	});
 });
+
+/**
+ * Declaration emit previously narrowed `$fetch` from `$fetch<JSONWebKeySet>(...)`,
+ * making `jwtClient()` unassignable to `BetterAuthClientPlugin` and collapsing
+ * `createAuthClient` option inference when combined with other plugins.
+ *
+ * @see https://github.com/masumi-network/sokosumi/pull/3403
+ */
+describe("jwtClient types", () => {
+	it("should be assignable to BetterAuthClientPlugin", () => {
+		const plugin: BetterAuthClientPlugin = jwtClient();
+		const plugins: BetterAuthClientPlugin[] = [jwtClient()];
+		expect(plugin.id).toBe("better-auth-client");
+		expect(plugins).toHaveLength(1);
+	});
+
+	it("should preserve additional user fields when combined with inferAdditionalFields", () => {
+		const client = createAuthClient({
+			plugins: [
+				inferAdditionalFields({
+					user: {
+						logo: {
+							type: "string",
+							required: false,
+						},
+					},
+				}),
+				jwtClient(),
+			],
+		});
+
+		type UpdateUserBody = NonNullable<Parameters<typeof client.updateUser>[0]>;
+
+		const body = {
+			logo: "https://example.com/logo.png",
+		} satisfies UpdateUserBody;
+		expect(body.logo).toBe("https://example.com/logo.png");
+		expectTypeOf<UpdateUserBody>().toMatchTypeOf<{
+			logo?: string | null | undefined;
+		}>();
+		expectTypeOf(client.jwks).toBeFunction();
+	});
+});