📝 update doc

README.md

@@ -4,6 +4,15 @@
 
 traq-oauth2 provides support for OAuth2 authentication in [traQ](https://github.com/traPtitech/traQ)
 
+## Features
+
+- [Authorization Code Flow](https://www.rfc-editor.org/rfc/rfc6749#section-1.3.1)
+  - Only this flow is supported in traQ.
+- [Proof Key for Code Exchange](https://www.rfc-editor.org/rfc/rfc7636)
+  - PKCE is supported in traQ.
+- Few dependencies
+  - traq-oauth2 only depends on [golang.org/x/oauth2](https://pkg.go.dev/golang.org/x/oauth2) and standard libraries.
+
 ## Installation
 
 ```bash

pkce.go

@@ -10,7 +10,7 @@ import (
 )
 
 // GenerateCodeVerifier generates a code verifier.
-// Ref: https://datatracker.ietf.org/doc/html/rfc7636#section-4.1
+// Ref: https://www.rfc-editor.org/rfc/rfc7636#section-4.1
 func GenerateCodeVerifier() (string, error) {
 	b := make([]byte, 32)
 	if _, err := rand.Read(b); err != nil {
@@ -41,7 +41,7 @@ func (m CodeChallengeMethod) String() string {
 }
 
 // GenerateCodeChallenge generates the code challenge from the code verifier.
-// Ref: https://datatracker.ietf.org/doc/html/rfc7636#section-4.2
+// Ref: https://www.rfc-editor.org/rfc/rfc7636#section-4.2
 func (m CodeChallengeMethod) GenerateCodeChallenge(codeVerifier string) (string, error) {
 	switch m {
 	case CodeChallengePlain:
@@ -61,7 +61,7 @@ func WithCodeChallenge(codeChallenge string) oauth2.AuthCodeOption {
 
 // WithCodeChallengeMethod sets the code_challenge_method parameter.
 // The default value is "plain".
-// If you want to use "S256", use WithCodeChallengeMethod(traqoauth2.CodeChallenge).
+// If you want to use "S256", use WithCodeChallengeMethod(traqoauth2.CodeChallengeS256).
 func WithCodeChallengeMethod(codeChallengeMethod CodeChallengeMethod) oauth2.AuthCodeOption {
 	return oauth2.SetAuthURLParam("code_challenge_method", codeChallengeMethod.String())
 }