Implement v4 endpoints for OAuth (#6040)

* Implement POST /oauth/apps endpoint for APIv4

* Implement GET /oauth/apps endpoint for APIv4

* Implement GET /oauth/apps/{app_id} and /oauth/apps/{app_id}/info endpoints for APIv4

* Refactor API version independent oauth endpoints

* Implement DELETE /oauth/apps/{app_id} endpoint for APIv4

* Implement /oauth/apps/{app_id}/regen_secret endpoint for APIv4

* Implement GET /user/{user_id}/oauth/apps/authorized endpoint for APIv4

* Implement POST /oauth/deauthorize endpoint

api4/context.go

@@ -382,6 +382,17 @@ func (c *Context) RequirePostId() *Context {
 	return c
 }
 
+func (c *Context) RequireAppId() *Context {
+	if c.Err != nil {
+		return c
+	}
+
+	if len(c.Params.AppId) != 26 {
+		c.SetInvalidUrlParam("app_id")
+	}
+	return c
+}
+
 func (c *Context) RequireFileId() *Context {
 	if c.Err != nil {
 		return c
@@ -464,6 +475,18 @@ func (c *Context) RequireCategory() *Context {
 	return c
 }
 
+func (c *Context) RequireService() *Context {
+	if c.Err != nil {
+		return c
+	}
+
+	if len(c.Params.Service) == 0 {
+		c.SetInvalidUrlParam("service")
+	}
+
+	return c
+}
+
 func (c *Context) RequirePreferenceName() *Context {
 	if c.Err != nil {
 		return c