FedCM登录与身份提供方治理（providers/mediation/nonce）最佳实践

背景与价值FedCM提供原生的联邦登录能力。合理治理providers与mediation并绑定nonce，可提升安全与用户体验。统一规范providers白名单：仅允许受控配置端点与client_id。mediation策略：默认 `required`，避免静默与无感授权。nonce绑定：服务端下发挑战，客户端回传绑定，防重放。核心实现调用示例（兼容性占位）type Provider = { configURL: string; clientId: string } const allowProviders = new Set(['https://idp.example.com/.well-known/openid-federation']) function providerAllowed(p: Provider): boolean { try { const u = new URL(p.configURL); return allowProviders.has(u.origin + u.pathname) } catch { return false } } async function fedcmLogin(providers: Provider[], nonce: string): Promise<any | null> { const list = providers.filter(providerAllowed) if (list.length === 0) return null if (!('credentials' in navigator)) return null try { const cred = await (navigator as any).credentials.get({ identity: { providers: list, mediation: 'required', nonce } }) return cred } catch { return null } } 落地建议在受控provider白名单下启用FedCM，并以 `mediation=required` 与nonce绑定完成安全登录。服务端验证返回的身份断言并执行rpId校验与时间窗口。验证清单providers是否命中白名单；mediation是否为required；nonce是否与服务端挑战一致。