Fix exchange bind json error

Signed-off-by: Asai Neko <sugar@sne.moe>

service/auth/exchange.go

@@ -1,6 +1,7 @@
 package auth
 
 import (
+	"fmt"
 	"net/url"
 	"nixcn-cms/data"
 	"nixcn-cms/pkgs/authcode"
@@ -17,8 +18,9 @@ func Exchange(c *gin.Context) {
 		State       string `json:"state"`
 	}
 
-	err := c.BindJSON(exchangeReq)
+	err := c.BindJSON(&exchangeReq)
 	if err != nil {
+		fmt.Println(err)
 		utils.HttpResponse(c, 400, "", "invalid request")
 		return
 	}