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pkce.go
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pkce.go
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// Proof Key for Code Exchange (PKCE) helps public clients to get access tokens and refresh tokens. PKCE is based on
// RFC7636, more on that can be found at https://tools.ietf.org/html/rfc7636 and https://auth0.com/docs/flows/authorization-code-flow-with-proof-key-for-code-exchange-pkce.
package pkce
import (
"crypto/sha256"
"encoding/base64"
"errors"
)
type Pkce struct {
// Optional, RandomString, this will be converted to Pkce.ChallengeCode
RandomString string
// Optional, Length of the Pkce.VerifyCode. When RandomString is provided, the Length is ignored.
// The value should be minimum 43 and maximum 128.
Length int
}
// When Pkce.RandomString is provided, VerifyCode is similar to it
// if not, VerifyCode returns a random string based on Pkce.Length.
func (p *Pkce) VerifyCode() (string, error) {
if p.RandomString == "" {
if p.Length == 0 {
return "", errors.New("length should be greater than 0")
}
if p.Length < 43 || p.Length > 128 {
return "", errors.New("length should be >=43 and <=128")
}
randomString := GenerateRandomString(p.Length)
p.RandomString = randomString
return randomString, nil
} else {
if len(p.RandomString) < 43 || len(p.RandomString) > 128 {
return "", errors.New("length should be >=43 and <=128")
}
return p.RandomString, nil
}
}
// ChallengeCode returns a challenge code as mentioned in https://tools.ietf.org/html/rfc7636#section-4.2.
// The code is based on
// code_challenge = BASE64URL-ENCODE(SHA256(ASCII(code_verifier)))
func (p *Pkce) ChallengeCode() (string, error) {
if p.RandomString == "" {
code, err := p.VerifyCode()
if err != nil {
return "", err
}
p.RandomString = code
}
hash := sha256.Sum256([]byte(p.RandomString))
toBase64 := base64.RawURLEncoding.EncodeToString(hash[:])
return toBase64, nil
}