feat(op): implemented support for client_credentials grant (#172)

* implemented support for client_credentials grant

* first draft

* Update pkg/op/token_client_credentials.go

Co-authored-by: Livio Amstutz <livio.a@gmail.com>

* updated placeholder interface name

* updated import paths

* ran mockgen

Co-authored-by: Livio Amstutz <livio.a@gmail.com>

pkg/op/config.go

@@ -27,6 +27,7 @@ type Configuration interface {
 	GrantTypeRefreshTokenSupported() bool
 	GrantTypeTokenExchangeSupported() bool
 	GrantTypeJWTAuthorizationSupported() bool
+	GrantTypeClientCredentialsSupported() bool
 	IntrospectionAuthMethodPrivateKeyJWTSupported() bool
 	IntrospectionEndpointSigningAlgorithmsSupported() []string
 	RevocationAuthMethodPrivateKeyJWTSupported() bool

pkg/op/discovery.go

@@ -75,6 +75,9 @@ func GrantTypes(c Configuration) []oidc.GrantType {
 	if c.GrantTypeRefreshTokenSupported() {
 		grantTypes = append(grantTypes, oidc.GrantTypeRefreshToken)
 	}
+	if c.GrantTypeClientCredentialsSupported() {
+		grantTypes = append(grantTypes, oidc.GrantTypeClientCredentials)
+	}
 	if c.GrantTypeTokenExchangeSupported() {
 		grantTypes = append(grantTypes, oidc.GrantTypeTokenExchange)
 	}

pkg/op/mock/authorizer.mock.go

@@ -7,9 +7,9 @@ package mock
 import (
 	reflect "reflect"
 
+	gomock "github.com/golang/mock/gomock"
 	http "github.com/zitadel/oidc/pkg/http"
 	op "github.com/zitadel/oidc/pkg/op"
-	gomock "github.com/golang/mock/gomock"
 )
 
 // MockAuthorizer is a mock of Authorizer interface.

pkg/op/mock/client.mock.go

@@ -8,9 +8,9 @@ import (
 	reflect "reflect"
 	time "time"
 
+	gomock "github.com/golang/mock/gomock"
 	oidc "github.com/zitadel/oidc/pkg/oidc"
 	op "github.com/zitadel/oidc/pkg/op"
-	gomock "github.com/golang/mock/gomock"
 )
 
 // MockClient is a mock of Client interface.

pkg/op/mock/configuration.mock.go

@@ -7,8 +7,8 @@ package mock
 import (
 	reflect "reflect"
 
-	op "github.com/zitadel/oidc/pkg/op"
 	gomock "github.com/golang/mock/gomock"
+	op "github.com/zitadel/oidc/pkg/op"
 	language "golang.org/x/text/language"
 )
 
@@ -105,6 +105,20 @@ func (mr *MockConfigurationMockRecorder) EndSessionEndpoint() *gomock.Call {
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "EndSessionEndpoint", reflect.TypeOf((*MockConfiguration)(nil).EndSessionEndpoint))
 }
 
+// GrantTypeClientCredentialsSupported mocks base method.
+func (m *MockConfiguration) GrantTypeClientCredentialsSupported() bool {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "GrantTypeClientCredentialsSupported")
+	ret0, _ := ret[0].(bool)
+	return ret0
+}
+
+// GrantTypeClientCredentialsSupported indicates an expected call of GrantTypeClientCredentialsSupported.
+func (mr *MockConfigurationMockRecorder) GrantTypeClientCredentialsSupported() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "GrantTypeClientCredentialsSupported", reflect.TypeOf((*MockConfiguration)(nil).GrantTypeClientCredentialsSupported))
+}
+
 // GrantTypeJWTAuthorizationSupported mocks base method.
 func (m *MockConfiguration) GrantTypeJWTAuthorizationSupported() bool {
 	m.ctrl.T.Helper()

pkg/op/mock/storage.mock.go

@@ -9,9 +9,9 @@ import (
 	reflect "reflect"
 	time "time"
 
+	gomock "github.com/golang/mock/gomock"
 	oidc "github.com/zitadel/oidc/pkg/oidc"
 	op "github.com/zitadel/oidc/pkg/op"
-	gomock "github.com/golang/mock/gomock"
 	jose "gopkg.in/square/go-jose.v2"
 )
 

pkg/op/op.go

@@ -229,6 +229,11 @@ func (o *openidProvider) GrantTypeJWTAuthorizationSupported() bool {
 	return true
 }
 
+func (o *openidProvider) GrantTypeClientCredentialsSupported() bool {
+	_, ok := o.storage.(ClientCredentialsStorage)
+	return ok
+}
+
 func (o *openidProvider) IntrospectionAuthMethodPrivateKeyJWTSupported() bool {
 	return true
 }

pkg/op/storage.go

@@ -27,6 +27,10 @@ type AuthStorage interface {
 	GetKeySet(context.Context) (*jose.JSONWebKeySet, error)
 }
 
+type ClientCredentialsStorage interface {
+	ClientCredentialsTokenRequest(ctx context.Context, clientID string, scopes []string) (TokenRequest, error)
+}
+
 type OPStorage interface {
 	GetClientByClientID(ctx context.Context, clientID string) (Client, error)
 	AuthorizeClientIDSecret(ctx context.Context, clientID, clientSecret string) error

pkg/op/token_client_credentials.go

@@ -0,0 +1,115 @@
+package op
+
+import (
+	"context"
+	"net/http"
+	"net/url"
+
+	httphelper "github.com/zitadel/oidc/pkg/http"
+	"github.com/zitadel/oidc/pkg/oidc"
+)
+
+//ClientCredentialsExchange handles the OAuth 2.0 client_credentials grant, including
+//parsing, validating, authorizing the client and finally returning a token
+func ClientCredentialsExchange(w http.ResponseWriter, r *http.Request, exchanger Exchanger) {
+	request, err := ParseClientCredentialsRequest(r, exchanger.Decoder())
+	if err != nil {
+		RequestError(w, r, err)
+	}
+
+	validatedRequest, client, err := ValidateClientCredentialsRequest(r.Context(), request, exchanger)
+	if err != nil {
+		RequestError(w, r, err)
+		return
+	}
+
+	resp, err := CreateClientCredentialsTokenResponse(r.Context(), validatedRequest, exchanger, client)
+	if err != nil {
+		RequestError(w, r, err)
+		return
+	}
+
+	httphelper.MarshalJSON(w, resp)
+}
+
+//ParseClientCredentialsRequest parsed the http request into a oidc.ClientCredentialsRequest
+func ParseClientCredentialsRequest(r *http.Request, decoder httphelper.Decoder) (*oidc.ClientCredentialsRequest, error) {
+	err := r.ParseForm()
+	if err != nil {
+		return nil, oidc.ErrInvalidRequest().WithDescription("error parsing form").WithParent(err)
+	}
+
+	request := new(oidc.ClientCredentialsRequest)
+	err = decoder.Decode(request, r.Form)
+	if err != nil {
+		return nil, oidc.ErrInvalidRequest().WithDescription("error decoding form").WithParent(err)
+	}
+
+	if clientID, clientSecret, ok := r.BasicAuth(); ok {
+		clientID, err = url.QueryUnescape(clientID)
+		if err != nil {
+			return nil, oidc.ErrInvalidClient().WithDescription("invalid basic auth header").WithParent(err)
+		}
+
+		clientSecret, err = url.QueryUnescape(clientSecret)
+		if err != nil {
+			return nil, oidc.ErrInvalidClient().WithDescription("invalid basic auth header").WithParent(err)
+		}
+
+		request.ClientID = clientID
+		request.ClientSecret = clientSecret
+	}
+
+	return request, nil
+}
+
+//ValidateClientCredentialsRequest validates the refresh_token request parameters including authorization check of the client
+//and returns the data representing the original auth request corresponding to the refresh_token
+func ValidateClientCredentialsRequest(ctx context.Context, request *oidc.ClientCredentialsRequest, exchanger Exchanger) (TokenRequest, Client, error) {
+	storage, ok := exchanger.Storage().(ClientCredentialsStorage)
+	if !ok {
+		return nil, nil, oidc.ErrUnsupportedGrantType().WithDescription("client_credentials grant not supported")
+	}
+
+	client, err := AuthorizeClientCredentialsClient(ctx, request, exchanger)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	tokenRequest, err := storage.ClientCredentialsTokenRequest(ctx, request.ClientID, request.Scope)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return tokenRequest, client, nil
+}
+
+func AuthorizeClientCredentialsClient(ctx context.Context, request *oidc.ClientCredentialsRequest, exchanger Exchanger) (Client, error) {
+	if err := AuthorizeClientIDSecret(ctx, request.ClientID, request.ClientSecret, exchanger.Storage()); err != nil {
+		return nil, err
+	}
+
+	client, err := exchanger.Storage().GetClientByClientID(ctx, request.ClientID)
+	if err != nil {
+		return nil, oidc.ErrInvalidClient().WithParent(err)
+	}
+
+	if !ValidateGrantType(client, oidc.GrantTypeClientCredentials) {
+		return nil, oidc.ErrUnauthorizedClient()
+	}
+
+	return client, nil
+}
+
+func CreateClientCredentialsTokenResponse(ctx context.Context, tokenRequest TokenRequest, creator TokenCreator, client Client) (*oidc.AccessTokenResponse, error) {
+	accessToken, _, validity, err := CreateAccessToken(ctx, tokenRequest, AccessTokenTypeJWT, creator, client, "")
+	if err != nil {
+		return nil, err
+	}
+
+	return &oidc.AccessTokenResponse{
+		AccessToken: accessToken,
+		TokenType:   oidc.BearerToken,
+		ExpiresIn:   uint64(validity.Seconds()),
+	}, nil
+}

pkg/op/token_request.go

@@ -20,6 +20,7 @@ type Exchanger interface {
 	GrantTypeRefreshTokenSupported() bool
 	GrantTypeTokenExchangeSupported() bool
 	GrantTypeJWTAuthorizationSupported() bool
+	GrantTypeClientCredentialsSupported() bool
 }
 
 func tokenHandler(exchanger Exchanger) func(w http.ResponseWriter, r *http.Request) {
@@ -44,6 +45,11 @@ func tokenHandler(exchanger Exchanger) func(w http.ResponseWriter, r *http.Reque
 				TokenExchange(w, r, exchanger)
 				return
 			}
+		case string(oidc.GrantTypeClientCredentials):
+			if exchanger.GrantTypeClientCredentialsSupported() {
+				ClientCredentialsExchange(w, r, exchanger)
+				return
+			}
 		case "":
 			RequestError(w, r, oidc.ErrInvalidRequest().WithDescription("grant_type missing"))
 			return