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/**
* Copyright 2014 Paul Querna
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
// Package otp implements both HOTP and TOTP based
// one time passcodes in a Google Authenticator compatible manner.
//
// When adding a TOTP for a user, you must store the "secret" value
// persistently. It is recommend to store the secret in an encrypted field in your
// datastore. Due to how TOTP works, it is not possible to store a hash
// for the secret value like you would a password.
//
// To enroll a user, you must first generate an OTP for them. Google
// Authenticator supports using a QR code as an enrollment method:
//
// import (
// "github.com/pquerna/otp/totp"
//
// "bytes"
// "image/png"
// )
//
// key, err := totp.Generate(totp.GenerateOpts{
// Issuer: "Example.com",
// AccountName: "alice@example.com",
// })
//
// // Convert TOTP key into a QR code encoded as a PNG image.
// var buf bytes.Buffer
// img, err := key.Image(200, 200)
// png.Encode(&buf, img)
//
// // display the QR code to the user.
// display(buf.Bytes())
//
// // Now Validate that the user's successfully added the passcode.
// passcode := promptForPasscode()
// valid := totp.Validate(passcode, key.Secret())
//
// if valid {
// // User successfully used their TOTP, save it to your backend!
// storeSecret("alice@example.com", key.Secret())
// }
//
// Validating a TOTP passcode is very easy, just prompt the user for a passcode
// and retrieve the associated user's previously stored secret.
// import "github.com/pquerna/otp/totp"
//
// passcode := promptForPasscode()
// secret := getSecret("alice@example.com")
//
// valid := totp.Validate(passcode, secret)
//
// if valid {
// // Success! continue login process.
// }
package otp
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