feat: Adds login via twitter

server/utils/pkce.go

@@ -0,0 +1,32 @@
+package utils
+
+import (
+	"crypto/sha256"
+	b64 "encoding/base64"
+	"math/rand"
+	"strings"
+	"time"
+)
+
+const (
+	length = 32
+)
+
+// GenerateCodeChallenge creates PKCE-Code-Challenge
+// and returns the verifier and challenge
+func GenerateCodeChallenge() (string, string) {
+	// Generate Verifier
+	randGenerator := rand.New(rand.NewSource(time.Now().UnixNano()))
+	randomBytes := make([]byte, length)
+	for i := 0; i < length; i++ {
+		randomBytes[i] = byte(randGenerator.Intn(255))
+	}
+	verifier := strings.Trim(b64.URLEncoding.EncodeToString(randomBytes), "=")
+
+	// Generate Challenge
+	rawChallenge := sha256.New()
+	rawChallenge.Write([]byte(verifier))
+	challenge := strings.Trim(b64.URLEncoding.EncodeToString(rawChallenge.Sum(nil)), "=")
+
+	return verifier, challenge
+}