diff --git a/lib/auth.ts b/lib/auth.ts
index fc8a38e..f7d9968 100644
--- a/lib/auth.ts
+++ b/lib/auth.ts
@@ -2,13 +2,15 @@
  * EncryptID Auth Store for rfunds-online
  *
  * Provides passkey-based identity for space creation and editing.
- * Uses Zustand with localStorage persistence.
+ * Uses Zustand with localStorage persistence, delegates WebAuthn ceremony to @encryptid/sdk.
  */
 
 import { create } from 'zustand'
 import { persist } from 'zustand/middleware'
+import { EncryptIDClient } from '@encryptid/sdk/client'
 
 const ENCRYPTID_SERVER = process.env.NEXT_PUBLIC_ENCRYPTID_SERVER_URL || 'https://encryptid.jeffemmett.com'
+const client = new EncryptIDClient(ENCRYPTID_SERVER)
 
 interface AuthState {
   isAuthenticated: boolean
@@ -22,17 +24,6 @@ interface AuthState {
   logout: () => void
 }
 
-function toBase64url(buffer: ArrayBuffer): string {
-  return btoa(String.fromCharCode(...new Uint8Array(buffer)))
-    .replace(/\+/g, '-')
-    .replace(/\//g, '_')
-    .replace(/=+$/, '')
-}
-
-function fromBase64url(str: string): Uint8Array {
-  return Uint8Array.from(atob(str.replace(/-/g, '+').replace(/_/g, '/')), c => c.charCodeAt(0))
-}
-
 export const useAuthStore = create<AuthState>()(
   persist(
     (set) => ({
@@ -45,48 +36,8 @@ export const useAuthStore = create<AuthState>()(
       login: async () => {
         set({ loading: true })
         try {
-          const startRes = await fetch(`${ENCRYPTID_SERVER}/api/auth/start`, {
-            method: 'POST',
-            headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify({}),
-          })
-          const { options } = await startRes.json()
-
-          const publicKeyOptions: PublicKeyCredentialRequestOptions = {
-            challenge: fromBase64url(options.challenge).buffer as ArrayBuffer,
-            rpId: options.rpId,
-            userVerification: options.userVerification as UserVerificationRequirement,
-            timeout: options.timeout,
-            allowCredentials: options.allowCredentials?.map((c: { type: string; id: string; transports: string[] }) => ({
-              type: c.type as PublicKeyCredentialType,
-              id: fromBase64url(c.id).buffer as ArrayBuffer,
-              transports: c.transports as AuthenticatorTransport[],
-            })),
-          }
-
-          const assertion = await navigator.credentials.get({ publicKey: publicKeyOptions }) as PublicKeyCredential
-          if (!assertion) throw new Error('Authentication cancelled')
-
-          const response = assertion.response as AuthenticatorAssertionResponse
-
-          const completeRes = await fetch(`${ENCRYPTID_SERVER}/api/auth/complete`, {
-            method: 'POST',
-            headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify({
-              challenge: options.challenge,
-              credential: {
-                credentialId: assertion.id,
-                authenticatorData: toBase64url(response.authenticatorData),
-                clientDataJSON: toBase64url(response.clientDataJSON),
-                signature: toBase64url(response.signature),
-                userHandle: response.userHandle ? toBase64url(response.userHandle) : null,
-              },
-            }),
-          })
-
-          const result = await completeRes.json()
-          if (!result.success) throw new Error(result.error || 'Authentication failed')
-
+          const result = await client.authenticate()
+          document.cookie = `encryptid_token=${result.token};path=/;max-age=900;SameSite=Lax`
           set({
             isAuthenticated: true,
             token: result.token,
@@ -103,52 +54,8 @@ export const useAuthStore = create<AuthState>()(
       register: async (username: string) => {
         set({ loading: true })
         try {
-          const startRes = await fetch(`${ENCRYPTID_SERVER}/api/register/start`, {
-            method: 'POST',
-            headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify({ username, displayName: username }),
-          })
-          const { options, userId } = await startRes.json()
-
-          const publicKeyOptions: PublicKeyCredentialCreationOptions = {
-            challenge: fromBase64url(options.challenge).buffer as ArrayBuffer,
-            rp: options.rp,
-            user: {
-              id: fromBase64url(options.user.id).buffer as ArrayBuffer,
-              name: options.user.name,
-              displayName: options.user.displayName,
-            },
-            pubKeyCredParams: options.pubKeyCredParams,
-            authenticatorSelection: options.authenticatorSelection,
-            timeout: options.timeout,
-            attestation: options.attestation as AttestationConveyancePreference,
-          }
-
-          const credential = await navigator.credentials.create({ publicKey: publicKeyOptions }) as PublicKeyCredential
-          if (!credential) throw new Error('Registration cancelled')
-
-          const response = credential.response as AuthenticatorAttestationResponse
-
-          const completeRes = await fetch(`${ENCRYPTID_SERVER}/api/register/complete`, {
-            method: 'POST',
-            headers: { 'Content-Type': 'application/json' },
-            body: JSON.stringify({
-              challenge: options.challenge,
-              userId,
-              username,
-              credential: {
-                credentialId: credential.id,
-                publicKey: toBase64url(response.getPublicKey?.() || response.attestationObject),
-                attestationObject: toBase64url(response.attestationObject),
-                clientDataJSON: toBase64url(response.clientDataJSON),
-                transports: (response as AuthenticatorAttestationResponse & { getTransports?: () => string[] }).getTransports?.() || [],
-              },
-            }),
-          })
-
-          const result = await completeRes.json()
-          if (!result.success) throw new Error(result.error || 'Registration failed')
-
+          const result = await client.register(username)
+          document.cookie = `encryptid_token=${result.token};path=/;max-age=900;SameSite=Lax`
           set({
             isAuthenticated: true,
             token: result.token,
@@ -163,6 +70,7 @@ export const useAuthStore = create<AuthState>()(
       },
 
       logout: () => {
+        document.cookie = 'encryptid_token=;path=/;max-age=0;SameSite=Lax'
         set({
           isAuthenticated: false,
           token: null,