Problems with oAuth/Bitbucket update from NetlifyCMS@2 to DecapCMS@3

Describe the bug

Current setup

We have a repository in Bitbucket Cloud that we use for storing the content as generated by NetlifyCMS@2. We have set up oAuth for the production using the auth_type='implicit in production. Meanwhile in development we access the CMS from http://localhost:3001/admin and the auth_type = undefined. This results in a call to API Netlify with https://api.netlify.com/auth?provider=bitbucket&site_id=cms.netlify.com&scope=repo which let's our developers to authenticate and enter in CMS.

Problem

One of the changes introduced in DecapCMS@3 is the change of the default site_domain used during the authentication. The site_domain (and consecutively the siteId) passed in the oAuth has changes from cms.netlify.com to demo.decapcms.org, this results in Not found response from https://api.netlify.com/auth?provider=bitbucket&site_id=demo.decapcms.org&scope=repo. As the demo.decapcms.org value is hardcoded for localhost, I can't override it.

If I search and replace all occurrences of demo.decapcms.org with cms.netlify.com, I am able to obtain the correct oAuth token and access into the CMS in localhost.

What am I supposed to do to enable access to CMS from localhost?

To Reproduce

Update dependencies from
- "netlify-cms-app": "^2.15.72" => "decap-cms-app": "^3.1.10"
- "netlify-cms-core": "^2.55.2" => "decap-cms": "^3.1.10"

Expected behavior

I expect to be able to authenticate and enter CMS from the local development environment running on http://localhost:3001/admin.

Screenshots demo.decapcms.org – failed login access

Applicable Versions:

Decap CMS version: 3.1.10
Git provider: Bitbucket
OS: MacOS 13.6.6, Ubuntu
Browser version brave 1.64.116
Node.JS version: 20.5.0
yarn 3.4.1

CMS configuration

Dynamic configuration

import type { CmsCollection } from 'decap-cms';
import type { ProductCmsConfig } from './types';
import type { EditorURLSearchParams } from 'web/app/admin/types';
import { components } from 'cms/collections/components';
import { sections } from 'cms/collections/sections';
import { pages } from 'cms/collections/pages';
import { commonPages } from 'cms/collections/commonPages';
import { commonProductPages } from 'cms/collections/commonProductPages';

const getCollections = async (
    product: string,
    theme: string,
): Promise<Object[]> => [
    { ...(await components(product, theme)) },
    { ...(await sections(product, theme)) },
    { ...pages(product, theme) },
    { ...commonPages },
    { ...commonProductPages(product) },
];

export const getConfig = async ({
    branch,
    product,
    theme,
}: EditorURLSearchParams): Promise<{ config: ProductCmsConfig }> => {
    const IS_PROD = process.env!.NODE_ENV === 'production';
    const IS_STAGE = process.env!.NEXT_PUBLIC_APP_ENV === 'stage';

    const app_id = IS_STAGE
        ? process.env!.NEXT_PUBLIC_CMS_APP_ID_STAGE
        : process.env!.NEXT_PUBLIC_CMS_APP_ID_PROD;
    return {
        config: {
            load_config_file: false,
            logo_url: '/common/logo.webp',
            backend: {
                open_authoring: true,
                name: 'bitbucket',
                branch: branch || process.env!.GIT_BRANCH,
                repo: process.env!.NEXT_PUBLIC_REPO,
                auth_type: IS_PROD ? 'implicit' : undefined,
                app_id,
                product,
                styleweb: theme,
                commit_messages: {
                    create: 'Create {{collection}} “{{slug}}”',
                    update: 'Update {{collection}} “{{slug}}”',
                    delete: 'Delete {{collection}} “{{slug}}”',
                    uploadMedia: '[skip ci] Upload “{{path}}”',
                    deleteMedia: '[skip ci] Delete “{{path}}”',
                },
                siteId: 'mydomain.com',
            },
            publish_mode: 'editorial_workflow',
            // allow_nesting: true,
            media_folder: `/${
                IS_PROD ? '' : 'public'
            }/${product}/${theme}/assets/`, // Media files will be stored here.
            public_folder: `/${product}/${theme}/assets`, // The src attribute for uploaded media will begin with this path.
            site_url: IS_PROD
                ? 'https://mydomain.com/editor'
                : 'http://localhost:3001/editor',
            collections: (await getCollections(
                product,
                theme,
            )) as CmsCollection[],
        },
    };
};

decaporg / decap-cms