has always been a separate Mini Program developer, this contact to open the platform, also registered, but also created applications, authorized their own testing of Mini Program.
then creates a Mini Program through developer tools that can also upload the code to the draft box of the open platform.

I have encountered problems in obtaining openid, and I don"t understand the concept of open platform all the time

    wx.login({
      success: res => {
        console.log(res)
        wx.showLoading({
          title: "",
        })
        wx.request({
          url: config.domain+"/api/login", 
          data: {
            code: res.code,
          },
          method:"post",
          success(res) {
            wx.hideLoading()
            self.globalData.user = res.data
            
          }
        })
        // console.log(config)
        //  res.code  openId, sessionKey, unionId
      }
    })

Mini Program only sends a code to my server here. How does the server know which Mini Program sent it?
ordinary development patterns are aimed at a Mini Program development, and the appid is fixed.