[management,client] Revert gRPC client secret removal (#5781)

* This reverts commit e5914e4e8b

Signed-off-by: bcmmbaga <bethuelmbaga12@gmail.com>

* Deprecate client secret in proto

Signed-off-by: bcmmbaga <bethuelmbaga12@gmail.com>

* Fix lint

Signed-off-by: bcmmbaga <bethuelmbaga12@gmail.com>

---------

Signed-off-by: bcmmbaga <bethuelmbaga12@gmail.com>

client/internal/auth/auth.go

@@ -221,6 +221,7 @@ func (a *Auth) getPKCEFlow(client *mgm.GrpcClient) (*PKCEAuthorizationFlow, erro
 	config := &PKCEAuthProviderConfig{
 		Audience:              protoConfig.GetAudience(),
 		ClientID:              protoConfig.GetClientID(),
+		ClientSecret:          protoConfig.GetClientSecret(), //nolint:staticcheck
 		TokenEndpoint:         protoConfig.GetTokenEndpoint(),
 		AuthorizationEndpoint: protoConfig.GetAuthorizationEndpoint(),
 		Scope:                 protoConfig.GetScope(),
@@ -265,6 +266,7 @@ func (a *Auth) getDeviceFlow(client *mgm.GrpcClient) (*DeviceAuthorizationFlow,
 	config := &DeviceAuthProviderConfig{
 		Audience:           protoConfig.GetAudience(),
 		ClientID:           protoConfig.GetClientID(),
+		ClientSecret:       protoConfig.GetClientSecret(), //nolint:staticcheck
 		Domain:             protoConfig.Domain,
 		TokenEndpoint:      protoConfig.GetTokenEndpoint(),
 		DeviceAuthEndpoint: protoConfig.GetDeviceAuthEndpoint(),

client/internal/auth/device_flow.go

@@ -29,6 +29,8 @@ var _ OAuthFlow = &DeviceAuthorizationFlow{}
 type DeviceAuthProviderConfig struct {
 	// ClientID An IDP application client id
 	ClientID string
+	// ClientSecret An IDP application client secret
+	ClientSecret string
 	// Domain An IDP API domain
 	// Deprecated. Use OIDCConfigEndpoint instead
 	Domain string

client/internal/auth/pkce_flow.go

@@ -38,6 +38,8 @@ const (
 type PKCEAuthProviderConfig struct {
 	// ClientID An IDP application client id
 	ClientID string
+	// ClientSecret An IDP application client secret
+	ClientSecret string
 	// Audience An Audience for to authorization validation
 	Audience string
 	// TokenEndpoint is the endpoint of an IDP manager where clients can obtain access token
@@ -109,7 +111,8 @@ func NewPKCEAuthorizationFlow(config PKCEAuthProviderConfig) (*PKCEAuthorization
 	}
 
 	cfg := &oauth2.Config{
-		ClientID: config.ClientID,
+		ClientID:     config.ClientID,
+		ClientSecret: config.ClientSecret,
 		Endpoint: oauth2.Endpoint{
 			AuthURL:  config.AuthorizationEndpoint,
 			TokenURL: config.TokenEndpoint,