使用Golang Gin框架遵循MVC模式构建API：获取授权信息并查询数据库

以下是一个可能的实现，仅供参考：

package main

import (
	"net/http"

	"github.com/gin-gonic/gin"
	"github.com/jinzhu/gorm"
	_ "github.com/jinzhu/gorm/dialects/mysql"
)

func main() {
	db, err := gorm.Open("mysql", "user:password@tcp(host:port)/database?charset=utf8mb4&parseTime=True&loc=Local")
	if err != nil {
		panic(err)
	}
	defer db.Close()

	db.AutoMigrate(&Balance{})

	r := gin.Default()

	balanceModel := NewBalanceModel(db)
	controller := NewController(balanceModel)

	r.Use(func(c *gin.Context) {
		auth := c.GetHeader("Authorization")
		if auth != "" {
			resp, err := http.Get("https://api.k.com/v2/p/")
			if err != nil {
				c.AbortWithError(http.StatusInternalServerError, err)
				return
			}
			defer resp.Body.Close()

			// TODO: parse JSON and extract username

			c.Set("username", username)
		}
	})

	r.GET("/balance", func(c *gin.Context) {
		username, ok := c.Get("username")
		if !ok {
			c.AbortWithStatus(http.StatusUnauthorized)
			return
		}

		balance, err := controller.GetBalance(username)
		if err != nil {
			c.AbortWithError(http.StatusInternalServerError, err)
			return
		}

		c.JSON(http.StatusOK, balance)
	})

	r.Run(":8080")
}

package main

import "github.com/jinzhu/gorm"

type Balance struct {
	ID           uint   `gorm:"primary_key"
	User         string `gorm:"unique_index"
	Money        uint
	Record       uint
	RecordDate   string
	Bot          uint
	BotDate      string
	MRecord      uint
	MRecordDate  string
	MRecordPack  uint
	CreatedAt    string
	UpdatedAt    string
	DeletedAt    *string `sql:"index"
}

type BalanceModel struct {
	db *gorm.DB
}

func NewBalanceModel(db *gorm.DB) *BalanceModel {
	return &BalanceModel{db: db}
}

func (m *BalanceModel) GetByUsername(username string) (*Balance, error) {
	var balance Balance
	if err := m.db.Where("user = ?", username).First(&balance).Error; err != nil {
		return nil, err
	}
	return &balance, nil
}

package main

import "errors"

type Controller struct {
	model *BalanceModel
}

func NewController(model *BalanceModel) *Controller {
	return &Controller{model: model}
}

func (c *Controller) GetBalance(username interface{}) (*Balance, error) {
	balance, err := c.model.GetByUsername(username.(string))
	if err != nil {
		return nil, err
	}
	if balance == nil {
		return nil, errors.New("balance not found")
	}
	return balance, nil
}

注意：这里的代码仅仅是一个示例，实际生产环境中还需要考虑很多问题，如错误处理、安全性、性能优化等。