totp secret option

src/totpChecker.ts

@@ -10,6 +10,7 @@ export interface ToTpGeneratorOptions {
     algorithm?: TotpAlgorithm;
     label?: string;
     secretLength?: number;
+    secret?: string;
     issuer: string;
 }
 
@@ -71,15 +72,18 @@ export class TotpChecker {
         return TotpChecker.DoGenerateCode(totpSecret, this.getCurrentPeriod(period), digits || 6, algorithm || "SHA-1").shift()!;
     }
 
+    public static GenerateSecret(secretLength?:number) {
+        secretLength = secretLength || 13;
+        return Array.from(crypto.randomBytes(secretLength)).map(x => RFC_4648[x % RFC_4648.length]).join("");
+    }
     public static GenerateUrl(optionsOrIssuer: ToTpGeneratorOptions | string): ToTpSecretAndUrl {
         let options: ToTpGeneratorOptions = typeof optionsOrIssuer === "string" ? { issuer: optionsOrIssuer } : optionsOrIssuer;
         options.digits = options.digits || 6;
         options.period = options.period || 30;
         options.algorithm = options.algorithm || "SHA-1";
         options.label = encodeURIComponent(options.label || options.issuer);
-        options.secretLength = options.secretLength || 13;
 
-        const secretStr = Array.from(crypto.randomBytes(options.secretLength)).map(x => RFC_4648[x % RFC_4648.length]).join("");
+        const secretStr = options.secret || TotpChecker.GenerateSecret(options.secretLength || 13)
         return {
             url: `otpauth://totp/${options.issuer}?issuer=${options.issuer}&secret=${secretStr}&digits=${options.digits}&period=${options.period}&algorithm=${options.algorithm}`,
             secret: secretStr