docs(example): implement OpenID Provider (#165)

* chore(example): implement OpenID Provider

* jwt profile and fixes

* some comments

* remove old op example

* fix code flow example

* add service user and update readme

* fix password for example use

* ignore example and mock folders for code coverage

* Update example/server/internal/storage.go

Co-authored-by: Silvan <silvan.reusser@gmail.com>

* Update client.go

Co-authored-by: Silvan <silvan.reusser@gmail.com>

example/server/internal/oidc.go

@@ -0,0 +1,203 @@
+package internal
+
+import (
+	"time"
+
+	"golang.org/x/text/language"
+
+	"github.com/caos/oidc/pkg/op"
+
+	"github.com/caos/oidc/pkg/oidc"
+)
+
+const (
+	//CustomScope is an example for how to use custom scopes in this library
+	//(in this scenario, when requested, it will return a custom claim)
+	CustomScope = "custom_scope"
+
+	//CustomClaim is an example for how to return custom claims with this library
+	CustomClaim = "custom_claim"
+)
+
+type AuthRequest struct {
+	ID            string
+	CreationDate  time.Time
+	ApplicationID string
+	CallbackURI   string
+	TransferState string
+	Prompt        []string
+	UiLocales     []language.Tag
+	LoginHint     string
+	MaxAuthAge    *time.Duration
+	UserID        string
+	Scopes        []string
+	ResponseType  oidc.ResponseType
+	Nonce         string
+	CodeChallenge *OIDCCodeChallenge
+
+	passwordChecked bool
+	authTime        time.Time
+}
+
+func (a *AuthRequest) GetID() string {
+	return a.ID
+}
+
+func (a *AuthRequest) GetACR() string {
+	return "" //we won't handle acr in this example
+}
+
+func (a *AuthRequest) GetAMR() []string {
+	//this example only uses password for authentication
+	if a.passwordChecked {
+		return []string{"pwd"}
+	}
+	return nil
+}
+
+func (a *AuthRequest) GetAudience() []string {
+	return []string{a.ApplicationID} //this example will always just use the client_id as audience
+}
+
+func (a *AuthRequest) GetAuthTime() time.Time {
+	return a.authTime
+}
+
+func (a *AuthRequest) GetClientID() string {
+	return a.ApplicationID
+}
+
+func (a *AuthRequest) GetCodeChallenge() *oidc.CodeChallenge {
+	return CodeChallengeToOIDC(a.CodeChallenge)
+}
+
+func (a *AuthRequest) GetNonce() string {
+	return a.Nonce
+}
+
+func (a *AuthRequest) GetRedirectURI() string {
+	return a.CallbackURI
+}
+
+func (a *AuthRequest) GetResponseType() oidc.ResponseType {
+	return a.ResponseType
+}
+
+func (a *AuthRequest) GetResponseMode() oidc.ResponseMode {
+	return "" //we won't handle response mode in this example
+}
+
+func (a *AuthRequest) GetScopes() []string {
+	return a.Scopes
+}
+
+func (a *AuthRequest) GetState() string {
+	return a.TransferState
+}
+
+func (a *AuthRequest) GetSubject() string {
+	return a.UserID
+}
+
+func (a *AuthRequest) Done() bool {
+	return a.passwordChecked //this example only uses password for authentication
+}
+
+func PromptToInternal(oidcPrompt oidc.SpaceDelimitedArray) []string {
+	prompts := make([]string, len(oidcPrompt))
+	for _, oidcPrompt := range oidcPrompt {
+		switch oidcPrompt {
+		case oidc.PromptNone,
+			oidc.PromptLogin,
+			oidc.PromptConsent,
+			oidc.PromptSelectAccount:
+			prompts = append(prompts, oidcPrompt)
+		}
+	}
+	return prompts
+}
+
+func MaxAgeToInternal(maxAge *uint) *time.Duration {
+	if maxAge == nil {
+		return nil
+	}
+	dur := time.Duration(*maxAge) * time.Second
+	return &dur
+}
+
+func authRequestToInternal(authReq *oidc.AuthRequest, userID string) *AuthRequest {
+	return &AuthRequest{
+		CreationDate:  time.Now(),
+		ApplicationID: authReq.ClientID,
+		CallbackURI:   authReq.RedirectURI,
+		TransferState: authReq.State,
+		Prompt:        PromptToInternal(authReq.Prompt),
+		UiLocales:     authReq.UILocales,
+		LoginHint:     authReq.LoginHint,
+		MaxAuthAge:    MaxAgeToInternal(authReq.MaxAge),
+		UserID:        userID,
+		Scopes:        authReq.Scopes,
+		ResponseType:  authReq.ResponseType,
+		Nonce:         authReq.Nonce,
+		CodeChallenge: &OIDCCodeChallenge{
+			Challenge: authReq.CodeChallenge,
+			Method:    string(authReq.CodeChallengeMethod),
+		},
+	}
+}
+
+type OIDCCodeChallenge struct {
+	Challenge string
+	Method    string
+}
+
+func CodeChallengeToOIDC(challenge *OIDCCodeChallenge) *oidc.CodeChallenge {
+	if challenge == nil {
+		return nil
+	}
+	challengeMethod := oidc.CodeChallengeMethodPlain
+	if challenge.Method == "S256" {
+		challengeMethod = oidc.CodeChallengeMethodS256
+	}
+	return &oidc.CodeChallenge{
+		Challenge: challenge.Challenge,
+		Method:    challengeMethod,
+	}
+}
+
+//RefreshTokenRequestFromBusiness will simply wrap the internal RefreshToken to implement the op.RefreshTokenRequest interface
+func RefreshTokenRequestFromBusiness(token *RefreshToken) op.RefreshTokenRequest {
+	return &RefreshTokenRequest{token}
+}
+
+type RefreshTokenRequest struct {
+	*RefreshToken
+}
+
+func (r *RefreshTokenRequest) GetAMR() []string {
+	return r.AMR
+}
+
+func (r *RefreshTokenRequest) GetAudience() []string {
+	return r.Audience
+}
+
+func (r *RefreshTokenRequest) GetAuthTime() time.Time {
+	return r.AuthTime
+}
+
+func (r *RefreshTokenRequest) GetClientID() string {
+	return r.ApplicationID
+}
+
+func (r *RefreshTokenRequest) GetScopes() []string {
+	return r.Scopes
+}
+
+func (r *RefreshTokenRequest) GetSubject() string {
+	return r.UserID
+}
+
+func (r *RefreshTokenRequest) SetCurrentScopes(scopes []string) {
+	r.Scopes = scopes
+}