我找到了一个解决方案。在第一次用户登录后，我保存令牌和刷新令牌，然后在应用程序组件（构造函数中）中创建一个方法，检查本地存储中是否有刷新令牌。如果有刷新令牌，则我调用firebase API，它会向我返回新令牌和新刷新令牌。以下是该方法的示例：

//the method
if (localStorage.getItem("refreshToken") != null) {
      console.log("refresh token not null");
      var request = {
        grant_type: "refresh_token",
        refresh_token: localStorage.getItem("refreshToken")
      };
      console.log("request...");
      this.http.post<RefreshTokenResponse>("https://securetoken.googleapis.com/v1/token?key=[YOUR_KEY]", request)
        .subscribe(x => {
          console.log(x.access_token);
          localStorage.setItem("token", x.access_token)
          console.log(x.refresh_token);
          localStorage.setItem("refreshToken", x.refresh_token);
        });
    }

export interface RefreshTokenResponse{
    access_token:string,
    refresh_token:string
}

export interface RefreshTokenRequest{
    grant_type: string;
    refresh_token:string;
}```