diff --git a/auth/api/http/groups/endpoint.go b/auth/api/http/groups/endpoint.go
index 26c3d31e..5315bb4b 100644
--- a/auth/api/http/groups/endpoint.go
+++ b/auth/api/http/groups/endpoint.go
@@ -250,7 +250,7 @@ func listMembersEndpoint(svc auth.Service) endpoint.Endpoint {
 			return memberPageRes{}, err
 		}
 
-		return buildUsersResponse(page), nil
+		return buildUsersResponse(page, req.groupType), nil
 	}
 }
 
@@ -350,7 +350,7 @@ func buildGroupsResponse(gp auth.GroupPage) groupPageRes {
 	return res
 }
 
-func buildUsersResponse(mp auth.MemberPage) memberPageRes {
+func buildUsersResponse(mp auth.MemberPage, groupType string) memberPageRes {
 	res := memberPageRes{
 		pageRes: pageRes{
 			Total:  mp.Total,
@@ -358,11 +358,12 @@ func buildUsersResponse(mp auth.MemberPage) memberPageRes {
 			Limit:  mp.Limit,
 			Name:   mp.Name,
 		},
-		Members: []interface{}{},
+		Type:    groupType,
+		Members: []string{},
 	}
 
 	for _, m := range mp.Members {
-		res.Members = append(res.Members, m)
+		res.Members = append(res.Members, m.ID)
 	}
 
 	return res
diff --git a/auth/api/http/groups/responses.go b/auth/api/http/groups/responses.go
index 39286645..cf6d373b 100644
--- a/auth/api/http/groups/responses.go
+++ b/auth/api/http/groups/responses.go
@@ -18,7 +18,8 @@ var (
 
 type memberPageRes struct {
 	pageRes
-	Members []interface{}
+	Type    string   `json:"type"`
+	Members []string `json:"members"`
 }
 
 func (res memberPageRes) Code() int {
diff --git a/auth/groups.go b/auth/groups.go
index ab9cd4ed..153a1e28 100644
--- a/auth/groups.go
+++ b/auth/groups.go
@@ -6,8 +6,12 @@ import (
 	"time"
 )
 
-const MaxLevel = uint64(5)
-const MinLevel = uint64(1)
+const (
+	// MaxLevel represents the maximum group hierarchy level.
+	MaxLevel = uint64(5)
+	// MinLevel represents the minimum group hierarchy level.
+	MinLevel = uint64(1)
+)
 
 var (
 	// ErrMaxLevelExceeded malformed entity.
@@ -50,13 +54,16 @@ var (
 	ErrMemberAlreadyAssigned = errors.New("member is already assigned")
 )
 
+// GroupMetadata defines the Metadata type.
 type GroupMetadata map[string]interface{}
 
+// Member represents the member information.
 type Member struct {
 	ID   string
 	Type string
 }
 
+// Group represents the group information.
 type Group struct {
 	ID          string
 	OwnerID     string
@@ -76,6 +83,7 @@ type Group struct {
 	UpdatedAt time.Time
 }
 
+// PageMetadata contains page metadata that helps navigation.
 type PageMetadata struct {
 	Total    uint64
 	Offset   uint64
@@ -87,16 +95,22 @@ type PageMetadata struct {
 	Metadata GroupMetadata
 }
 
+// GroupPage contains page related metadata as well as list of groups that
+// belong to this page.
 type GroupPage struct {
 	PageMetadata
 	Groups []Group
 }
 
+// MemberPage contains page related metadata as well as list of members that
+// belong to this page.
 type MemberPage struct {
 	PageMetadata
 	Members []Member
 }
 
+// GroupService specifies an API that must be fullfiled by the domain service
+// implementation, and all of its decorators (e.g. logging & metrics).
 type GroupService interface {
 	// CreateGroup creates new  group.
 	CreateGroup(ctx context.Context, token string, g Group) (Group, error)
@@ -135,6 +149,7 @@ type GroupService interface {
 	AssignGroupAccessRights(ctx context.Context, token, thingGroupID, userGroupID string) error
 }
 
+// GroupRepository specifies a group persistence API.
 type GroupRepository interface {
 	// Save group
 	Save(ctx context.Context, g Group) (Group, error)
diff --git a/users/api/responses.go b/users/api/responses.go
index 90238680..7e3a8b4f 100644
--- a/users/api/responses.go
+++ b/users/api/responses.go
@@ -19,8 +19,6 @@ var (
 	_ mainflux.Response = (*createGroupRes)(nil)
 	_ mainflux.Response = (*createUserRes)(nil)
 	_ mainflux.Response = (*deleteRes)(nil)
-	_ mainflux.Response = (*assignUserToGroupRes)(nil)
-	_ mainflux.Response = (*removeUserFromGroupRes)(nil)
 )
 
 // MailSent message response when link is sent
@@ -237,31 +235,3 @@ func (res deleteRes) Headers() map[string]string {
 func (res deleteRes) Empty() bool {
 	return true
 }
-
-type assignUserToGroupRes struct{}
-
-func (res assignUserToGroupRes) Code() int {
-	return http.StatusNoContent
-}
-
-func (res assignUserToGroupRes) Headers() map[string]string {
-	return map[string]string{}
-}
-
-func (res assignUserToGroupRes) Empty() bool {
-	return true
-}
-
-type removeUserFromGroupRes struct{}
-
-func (res removeUserFromGroupRes) Code() int {
-	return http.StatusNoContent
-}
-
-func (res removeUserFromGroupRes) Headers() map[string]string {
-	return map[string]string{}
-}
-
-func (res removeUserFromGroupRes) Empty() bool {
-	return true
-}