feat(auth): add account linking support for different email providers

apps/server/src/libs/auth.ts

@@ -575,6 +575,11 @@ export function createAuth(
     // https://github.com/better-auth/better-auth/issues/5892
     account: {
       skipStateCookieCheck: true,
+      accountLinking: {
+        // Product requirement: signed-in users may attach OAuth identities
+        // whose provider email differs from their AIRI account email.
+        allowDifferentEmails: true,
+      },
     },
 
     socialProviders: {

packages/stage-ui/src/composables/use-linked-accounts.test.ts

@@ -0,0 +1,55 @@
+import { describe, expect, it, vi } from 'vitest'
+import { createSSRApp, ref } from 'vue'
+import { renderToString } from 'vue/server-renderer'
+
+import { useLinkedAccounts } from './use-linked-accounts'
+
+describe('useLinkedAccounts', () => {
+  it('passes the profile page URL as the OAuth link error callback URL', async () => {
+    const linkSocial = vi.fn(async () => ({
+      data: { status: true, redirect: false },
+      error: null,
+    }))
+
+    const holder: {
+      linkedAccounts?: ReturnType<typeof useLinkedAccounts>
+    } = {}
+    const app = createSSRApp({
+      setup() {
+        holder.linkedAccounts = useLinkedAccounts({
+          client: {
+            listAccounts: vi.fn(async () => ({ data: [], error: null })),
+            unlinkAccount: vi.fn(async () => ({ data: null, error: null })),
+            linkSocial,
+          },
+          isAuthenticated: ref(false),
+          describeError: () => '',
+          buildCallbackURL: () => 'https://auth.airi.build/ui/profile',
+          messages: {
+            listFailed: 'list failed',
+            unlinkFailed: 'unlink failed',
+            linkFailed: 'link failed',
+            lastAccount: 'last account',
+            unlinked: provider => `${provider} unlinked`,
+            linkStarted: provider => `${provider} link started`,
+          },
+        })
+
+        return () => null
+      },
+    })
+
+    await renderToString(app)
+
+    if (!holder.linkedAccounts)
+      throw new Error('Expected linked accounts composable to initialize')
+
+    await holder.linkedAccounts.link('github', 'GitHub')
+
+    expect(linkSocial).toHaveBeenCalledWith({
+      provider: 'github',
+      callbackURL: 'https://auth.airi.build/ui/profile',
+      errorCallbackURL: 'https://auth.airi.build/ui/profile',
+    })
+  })
+})

packages/stage-ui/src/composables/use-linked-accounts.ts

@@ -196,6 +196,7 @@ export function useLinkedAccounts(args: UseLinkedAccountsArgs) {
       const { data, error: apiError } = await args.client.linkSocial({
         provider: providerId,
         callbackURL,
+        errorCallbackURL: callbackURL,
       })
       if (apiError)
         throw new Error(apiError.message ?? 'linkSocial failed')