PLT-6763 Implement user access tokens and new roles (server-side) (#6972)

* Implement user access tokens and new roles

* Update config.json

* Add public post permission to apiv3

* Remove old comment

* Fix model unit test

* Updates to store per feedback

* Updates per feedback from CS

model/user_access_token.go

@@ -0,0 +1,81 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+)
+
+type UserAccessToken struct {
+	Id          string `json:"id"`
+	Token       string `json:"token,omitempty"`
+	UserId      string `json:"user_id"`
+	Description string `json:"description"`
+}
+
+func (t *UserAccessToken) IsValid() *AppError {
+	if len(t.Id) != 26 {
+		return NewAppError("UserAccessToken.IsValid", "model.user_access_token.is_valid.id.app_error", nil, "", http.StatusBadRequest)
+	}
+
+	if len(t.Token) != 26 {
+		return NewAppError("UserAccessToken.IsValid", "model.user_access_token.is_valid.token.app_error", nil, "", http.StatusBadRequest)
+	}
+
+	if len(t.UserId) != 26 {
+		return NewAppError("UserAccessToken.IsValid", "model.user_access_token.is_valid.user_id.app_error", nil, "", http.StatusBadRequest)
+	}
+
+	if len(t.Description) > 255 {
+		return NewAppError("UserAccessToken.IsValid", "model.user_access_token.is_valid.description.app_error", nil, "", http.StatusBadRequest)
+	}
+
+	return nil
+}
+
+func (t *UserAccessToken) PreSave() {
+	t.Id = NewId()
+}
+
+func (t *UserAccessToken) ToJson() string {
+	b, err := json.Marshal(t)
+	if err != nil {
+		return ""
+	} else {
+		return string(b)
+	}
+}
+
+func UserAccessTokenFromJson(data io.Reader) *UserAccessToken {
+	decoder := json.NewDecoder(data)
+	var t UserAccessToken
+	err := decoder.Decode(&t)
+	if err == nil {
+		return &t
+	} else {
+		return nil
+	}
+}
+
+func UserAccessTokenListToJson(t []*UserAccessToken) string {
+	b, err := json.Marshal(t)
+	if err != nil {
+		return ""
+	} else {
+		return string(b)
+	}
+}
+
+func UserAccessTokenListFromJson(data io.Reader) []*UserAccessToken {
+	decoder := json.NewDecoder(data)
+	var t []*UserAccessToken
+	err := decoder.Decode(&t)
+	if err == nil {
+		return t
+	} else {
+		return nil
+	}
+}