nextauthjs/next-auth · error · UnknownAction

Unsupported action

Error message

Unsupported action

What it means

The built-in signin page handler throws UnknownAction("Unsupported action") when signin() is called with a providerId argument. A specific provider signin must be handled by rendering the provider list page or redirecting directly, not through this page action.

Source

Thrown at packages/core/src/lib/pages/index.ts:90

        value: "",
        options: { ...options.cookies.csrfToken.options, maxAge: 0 },
      })
      return { status: 404, cookies }
    },
    providers(providers: InternalProvider[]) {
      return {
        headers: { "Content-Type": "application/json" },
        body: providers.reduce<Record<string, PublicProvider>>(
          (acc, { id, name, type, signinUrl, callbackUrl }) => {
            acc[id] = { id, name, type, signinUrl, callbackUrl }
            return acc
          },
          {}
        ),
      }
    },
    signin(providerId?: string, error?: any) {
      if (providerId) throw new UnknownAction("Unsupported action")
      if (pages?.signIn) {
        let signinUrl = `${pages.signIn}${
          pages.signIn.includes("?") ? "&" : "?"
        }${new URLSearchParams({ callbackUrl: params.callbackUrl ?? "/" })}`
        if (error) signinUrl = `${signinUrl}&${new URLSearchParams({ error })}`
        return { redirect: signinUrl, cookies }
      }

      // If we have a webauthn provider with conditional UI and
      // a simpleWebAuthnBrowserScript is defined, we need to
      // render the script in the page.
      const webauthnProvider = providers?.find(
        (p): p is InternalProvider<"webauthn"> =>
          p.type === "webauthn" &&
          p.enableConditionalUI &&
          !!p.simpleWebAuthnBrowserVersion
      )

View on GitHub (pinned to a1a16a5a77)

Solutions

1. Link to /auth/signin (no provider id) on the sign-in page and trigger provider sign-in via the client signIn() helper
2. Use /auth/signin only for the provider-list page; start provider flows with signIn(providerId) from the browser
3. If you want direct provider redirects via URL, ensure pages.signIn is not intercepting that route

Example fix

// before
<a href="/auth/signin/github">Sign in with GitHub</a>  <!-- on custom pages.signIn -->
// after
<button onClick={() => signIn("github")}>Sign in with GitHub</button>

const providerMatch = pathname.match(/^\/auth\/signin\/(.+)$/); if (providerMatch && customSignInPageEnabled) throw new Error("Provider-specific signin must use client signIn(), not the sign-in page");

null

try { return await renderSignInPage(providerId) } catch (e) { if (String(e.message).includes("Unsupported action")) return Response.redirect("/auth/signin"); throw e; }

When it happens

Trigger: Requesting /auth/signin/<providerId> while the pages.signIn page is rendered (the signin page action receives a providerId), meaning the framework tried to route a provider-specific signin through the generic sign-in page handler.

Common situations: Custom page configuration where pages.signIn is set and a link points to /auth/signin/google instead of initiating signin via signIn('google') client-side; broken manual links on a custom sign-in page.

Related errors

• [updateSession] Failed to fetch updated session
• Object is nullish
• User not found
• Account not found
• Session not found

AI-assisted analysis of nextauthjs/next-auth@a1a16a5a77 (2026-08-28). Data as JSON: /api/errors/c485f930542b18db. Report an issue: GitHub.