When a cookie is protected with the secure attribute set to true it will not be send by the browser over an unencrypted HTTP
request and thus cannot be observed by an unauthorized person during a man-in-the-middle attack.
Ask Yourself Whether
  -  the cookie is for instance a session-cookie not designed to be sent over non-HTTPS communication. 
-  it’s not sure that the website contains mixed content or not
  (ie HTTPS everywhere or not) 
There is a risk if you answered yes to any of those questions.
Recommended Secure Coding Practices
  -  It is recommended to use HTTPseverywhere so setting thesecureflag to true should be the default behaviour
  when creating cookies.
-  Set the secureflag to true for session-cookies.
Sensitive Code Example
For Go Standard Library:
import "net/http"
func handler(w http.ResponseWriter, req *http.Request) {
    cookie := http.Cookie{}
    cookie.Name = "cookiename"
    cookie.Value = "cookievalue"
    http.SetCookie(w, &cookie) // Sensitive: Secure is false by default
}
For Beego:
import "github.com/beego/beego/v2/server/web"
func (ctrl *MainController) handler() {
    ctrl.Ctx.SetCookie("name1", "value1", 200, "/", "example.com", false, false) // Sensitive
}
For Fiber:
import "github.com/gofiber/fiber/v2"
func handler(c *fiber.Ctx) error {
    cookie := new(fiber.Cookie)
    cookie.Name = "name"
    cookie.Value = "value"
    c.Cookie(cookie) // Sensitive: Secure is false by default
    return c.SendString("")
}
For Gin:
import "github.com/gin-gonic/gin"
func handler(c *gin.Context) {
    c.SetCookie("name", "value", 200, "/", "example.com", false, false) // Sensitive
    c.JSON(http.StatusOK, gin.H{"message": ""})
}
Compliant Solution
For Go Standard Library:
import "net/http"
func handler(w http.ResponseWriter, req *http.Request) {
    cookie := http.Cookie{}
    cookie.Name = "cookiename"
    cookie.Value = "cookievalue"
    cookie.Secure = true
    http.SetCookie(w, &cookie)
}
For Beego:
import "github.com/beego/beego/v2/server/web"
func (ctrl *MainController) handler() {
    ctrl.Ctx.SetCookie("name1", "value1", 200, "/", "example.com", true, false)
}
For Fiber:
import "github.com/gofiber/fiber/v2"
func handler(c *fiber.Ctx) error {
    cookie := new(fiber.Cookie)
    cookie.Name = "name"
    cookie.Value = "value"
    cookie.Secure = true
    c.Cookie(cookie)
    return c.SendString("")
}
For Gin:
import "github.com/gin-gonic/gin"
func handler(c *gin.Context) {
    c.SetCookie("name", "value", 200, "/", "example.com", true, false)
    c.JSON(http.StatusOK, gin.H{"message": ""})
}
See