Go (Gin)

package main

import (
    "fmt"
    "io"
    "net/http"
    "net/url"
    "os"

    "github.com/gin-gonic/gin"
)

func BlockDisposable() gin.HandlerFunc {
    return func(c *gin.Context) {
        email := c.Query("email")
        if email == "" {
            email = c.PostForm("email")
        }
        if email == "" {
            c.Next()
            return
        }

        req, _ := http.NewRequest("GET",
            "https://api.disposableguard.com/v1/check", nil)
        q := req.URL.Query()
        q.Add("email", email)
        req.URL.RawQuery = q.Encode()
        req.Header.Set("Authorization", "Bearer "+os.Getenv("DG_KEY"))

        resp, err := http.DefaultClient.Do(req)
        if err != nil {
            c.Next() // fail-open
            return
        }
        defer resp.Body.Close()

        body, _ := io.ReadAll(resp.Body)
        // Parse JSON and check is_disposable field
        // For brevity, use a JSON library like encoding/json
        _ = body

        c.Next()
    }
}

func main() {
    r := gin.Default()
    r.POST("/signup", BlockDisposable(), signupHandler)
    r.Run()
}