feat: add non-interactive SSO login flow for embedded/iframe deployments (closes #69)

lib/oauth/cookie-config.ts

@@ -0,0 +1,11 @@
+const COOKIE_SAME_SITE = (process.env.COOKIE_SAME_SITE || 'lax') as 'lax' | 'none' | 'strict';
+
+export function getCookieOptions() {
+  return {
+    httpOnly: true,
+    secure: COOKIE_SAME_SITE === 'none' ? true : process.env.NODE_ENV === 'production',
+    sameSite: COOKIE_SAME_SITE,
+    path: '/',
+    maxAge: 30 * 24 * 60 * 60,
+  };
+}

lib/oauth/pkce-server.ts

@@ -0,0 +1,18 @@
+import { randomBytes, createHash } from 'node:crypto';
+
+function base64urlEncode(buffer: Buffer): string {
+  return buffer.toString('base64').replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
+}
+
+export function generateCodeVerifierServer(): string {
+  return base64urlEncode(randomBytes(32));
+}
+
+export function generateCodeChallengeServer(verifier: string): string {
+  const hash = createHash('sha256').update(verifier).digest();
+  return base64urlEncode(hash);
+}
+
+export function generateStateServer(): string {
+  return base64urlEncode(randomBytes(32));
+}

lib/oauth/token-exchange.ts

@@ -0,0 +1,88 @@
+import { logger } from '@/lib/logger';
+import { discoverOAuth } from '@/lib/oauth/discovery';
+import type { OAuthMetadata } from '@/lib/oauth/discovery';
+
+const CLIENT_SECRET = process.env.OAUTH_CLIENT_SECRET || '';
+
+export function getRequiredConfig() {
+  const clientId = process.env.OAUTH_CLIENT_ID;
+  const serverUrl = process.env.JMAP_SERVER_URL || process.env.NEXT_PUBLIC_JMAP_SERVER_URL;
+  const issuerUrl = process.env.OAUTH_ISSUER_URL;
+  if (!clientId || !serverUrl) {
+    throw new Error(`OAuth misconfigured: ${[!clientId && 'OAUTH_CLIENT_ID', !serverUrl && 'JMAP_SERVER_URL'].filter(Boolean).join(', ')} not set`);
+  }
+  const discoveryUrl = issuerUrl?.trim() || serverUrl;
+  if (issuerUrl !== undefined && !issuerUrl.trim()) {
+    logger.warn('OAUTH_ISSUER_URL is set but empty, falling back to JMAP_SERVER_URL for discovery');
+  }
+  return { clientId, serverUrl, discoveryUrl };
+}
+
+export async function getTokenEndpoint(): Promise<string> {
+  const { discoveryUrl } = getRequiredConfig();
+  const metadata = await discoverOAuth(discoveryUrl);
+  if (!metadata?.token_endpoint) {
+    throw new Error('OAuth token endpoint not found');
+  }
+  return metadata.token_endpoint;
+}
+
+export async function getMetadata(): Promise<OAuthMetadata | null> {
+  const { discoveryUrl } = getRequiredConfig();
+  return discoverOAuth(discoveryUrl);
+}
+
+export function buildOAuthParams(base: Record<string, string>): URLSearchParams {
+  const { clientId } = getRequiredConfig();
+  const params = new URLSearchParams({ ...base, client_id: clientId });
+  if (CLIENT_SECRET) {
+    params.set('client_secret', CLIENT_SECRET);
+  }
+  return params;
+}
+
+export interface TokenResult {
+  access_token: string;
+  expires_in: number;
+  refresh_token?: string;
+}
+
+export async function exchangeCodeForTokens(
+  code: string,
+  codeVerifier: string,
+  redirectUri: string,
+): Promise<TokenResult> {
+  const tokenEndpoint = await getTokenEndpoint();
+
+  const params = buildOAuthParams({
+    grant_type: 'authorization_code',
+    code,
+    redirect_uri: redirectUri,
+    code_verifier: codeVerifier,
+  });
+
+  const tokenResponse = await fetch(tokenEndpoint, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body: params.toString(),
+  });
+
+  if (!tokenResponse.ok) {
+    const errorText = await tokenResponse.text();
+    logger.error('Token exchange failed', { status: tokenResponse.status, error: errorText });
+    throw new Error('Token exchange failed');
+  }
+
+  const tokens = await tokenResponse.json();
+
+  if (!tokens.access_token) {
+    logger.error('Token response missing access_token', { response: JSON.stringify(tokens).substring(0, 500) });
+    throw new Error('Invalid token response');
+  }
+
+  return {
+    access_token: tokens.access_token,
+    expires_in: tokens.expires_in || 3600,
+    refresh_token: tokens.refresh_token,
+  };
+}