signIn

The signIn client function is the primary programmatic entry point for initiating an authentication flow with any configured OAuth 2.0 or OpenID Connect (OIDC) provider, from a client-side or browser context.

sign-in.ts

import { authClient } from "@/lib/auth-client"

const output = await authClient.signIn("google", {
  redirectTo: "/dashboard",
})

Reference

Parameters

Parameter	Type	Required	Description
providerId	`string`	Yes	The id of the OAuth provider to use for sign-in.
options	`SignInOptions`	No	An object containing additional options for the sign-in process.

SignInOptions

Option	Type	Default	Description
redirect	`boolean`	`false`	Whether to redirect via `window.location.assign` (`true`) or return the result as an object (`false`).
redirectTo	`string`	undefined	The URL to redirect to after a successful sign-in.

redirect defaults to false here — unlike the other client methods, which default to true. This is intentional: signIn navigates the browser to a cross-origin OAuth provider URL, and doing that via a Location header on a fetch() response runs into CORS restrictions on cross-origin redirects. To avoid that, the client resolves the authorize URL and navigates manually with window.location.assign, which requires you to opt in or handle the navigation yourself.

Returns

Return Type	Description
`Promise<SignInReturn<Options>>`	Resolves to an object containing `signInURL`, `redirect`, and `success` — see Behavior below.

Behavior

Cookies are set automatically in the browser context — you don't need to handle them manually.
The return value depends on the redirect option:
- redirect: false (default) — resolves to an object with signInURL, redirect: false, and success, letting you handle navigation yourself.
- redirect: true — the client navigates the browser to the OAuth provider's authorize URL via window.location.assign. Nothing meaningful is returned to inspect programmatically; the navigation itself is the result.
If sign-in fails to initiate (e.g. an unknown providerId), signInURL resolves to null and success is false.

Usage

social-login.ts

import { authClient } from "@/lib/auth-client"

const output = await authClient.signIn("github", {
  redirect: true,
  redirectTo: "/dashboard",
})

manual-navigation.ts

import { authClient } from "@/lib/auth-client"

const output = await authClient.signIn("google")

if (output.success) {
  window.location.assign(output.signInURL)
}