Restructure project layout

internal/authentication/token.go

@@ -0,0 +1,54 @@
+package authentication
+
+import (
+	"crypto/rand"
+	"math/big"
+)
+
+var (
+	tokenCharacters   = []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
+	randomTokenLength = 64
+	applicationPrefix = "A"
+)
+
+func randIntn(n int) int {
+	max := big.NewInt(int64(n))
+
+	res, err := rand.Int(rand.Reader, max)
+	if err != nil {
+		panic("random source is not available")
+	}
+
+	return int(res.Int64())
+}
+
+// GenerateNotExistingToken receives a token generation function and a function to check whether the token exists, returns a unique token.
+func GenerateNotExistingToken(generateToken func() string, tokenExists func(token string) bool) string {
+	for {
+		token := generateToken()
+
+		if !tokenExists(token) {
+			return token
+		}
+	}
+}
+
+func generateRandomString(length int) string {
+	res := make([]byte, length)
+
+	for i := range res {
+		index := randIntn(len(tokenCharacters))
+		res[i] = tokenCharacters[index]
+	}
+
+	return string(res)
+}
+
+func generateRandomToken(prefix string) string {
+	return prefix + generateRandomString(randomTokenLength)
+}
+
+// GenerateApplicationToken generates a token for an application.
+func GenerateApplicationToken() string {
+	return generateRandomToken(applicationPrefix)
+}