fix: update AuthInstance type to use AuthOptions for better type inference

src/runtime/server/utils/auth.ts

@@ -11,7 +11,8 @@ import { useRuntimeConfig } from 'nitropack/runtime'
 import { withoutProtocol } from 'ufo'
 import { resolveCustomSecondaryStorageRequirement } from './custom-secondary-storage'
 
-type AuthInstance = ReturnType<typeof betterAuth>
+type AuthOptions = ReturnType<typeof createServerAuth>
+type AuthInstance = ReturnType<typeof betterAuth<AuthOptions>>
 
 const _authCache = new Map<string, AuthInstance>()
 let _baseURLInferenceLogged = false

test/cases/plugins-type-inference/server/auth.config.ts

@@ -1,3 +1,4 @@
+import { username } from 'better-auth/plugins'
 import { defineServerAuth } from '../../../../src/runtime/config'
 
 function customAdminLikePlugin() {
@@ -25,7 +26,7 @@ function customAdminLikePlugin() {
 
 export default defineServerAuth({
   emailAndPassword: { enabled: true },
-  plugins: [customAdminLikePlugin()] as const,
+  plugins: [customAdminLikePlugin(), username()] as const,
   user: {
     additionalFields: {
       internalCode: {

test/cases/plugins-type-inference/typecheck-target.ts

@@ -1,6 +1,8 @@
 import type { AuthUser } from '#nuxt-better-auth'
 import type { NitroRouteRules } from 'nitropack/types'
 
+declare const serverAuth: typeof import('../../../src/runtime/server/utils/auth').serverAuth
+
 declare module '#nuxt-better-auth' {
   interface AuthUser {
     foo: string
@@ -25,5 +27,10 @@ const rules: NitroRouteRules = {
   },
 }
 
+const auth = serverAuth()
+const signInUsername = auth.api.signInUsername
+
 void user
 void rules
+void auth
+void signInUsername

test/infer-plugins-types.test.ts

@@ -8,8 +8,8 @@ const env = {
   BETTER_AUTH_SECRET: 'test-secret-for-testing-only-32chars',
 }
 
-describe('type inference regression #107', () => {
-  it('typechecks routeRules user fields inferred from plugins/additionalFields', () => {
+describe('type inference regressions #107 and #192', () => {
+  it('typechecks plugin/additional fields and serverAuth plugin API inference', () => {
     const prepare = spawnSync('npx', ['nuxi', 'prepare'], {
       cwd: fixtureDir,
       env,
@@ -28,5 +28,7 @@ describe('type inference regression #107', () => {
     expect(output).not.toContain(`is not assignable to type 'BetterAuthPlugin'`)
     expect(output).not.toContain(`'role' does not exist in type`)
     expect(output).not.toContain(`'internalCode' does not exist in type`)
+    expect(output).not.toContain(`Property 'signInUsername' does not exist on type`)
+    expect(output).not.toContain(`'signInUsername' does not exist on type`)
   }, 60_000)
 })