The correct answer is A. Create an AWS Service Catalog portfolio in the organization’s management account. Upload the CloudFormation template. Add the template to the portfolio’s product list. Share the portfolio with the OU.

According to the AWS documentation, AWS Service Catalog is a service that allows you to create and manage catalogs of IT services that are approved for use on AWS. You can use Service Catalog to centrally manage commonly deployed IT services and help achieve consistent governance and compliance requirements, while enabling users to quickly deploy only the approved IT services they need.

To use Service Catalog with multiple AWS accounts, you need to enable AWS Organizations with all features enabled. This allows you to centrally manage your accounts and apply policies across your organization. You can also use Service Catalog as a service principal for AWS Organizations, which lets you share your portfolios with organizational units (OUs) or accounts in your organization.

To create a Service Catalog portfolio, you need to use an administrator account, such as the organization’s management account. You can upload your CloudFormation template as a product in your portfolio, and define constraints and tags for it. You can then share your portfolio with the OU that contains the accounts for the web applications. This will allow the developers in those accounts to launch products from the shared portfolio using the Service Catalog end user console.

Option B is incorrect because CloudFormation modules are reusable components that encapsulate one or more resources and their configurations. They are not meant to be used as templates for deploying entire stacks of resources. Moreover, sharing a module with an OU does not grant access to launch stacks from it.

Option C is incorrect because creating an IAM role that has a trust policy that allows cross-account access to the portfolio is not secure. It would allow any user in the OU accounts to assume the role and access the portfolio, regardless of their job function or access requirements.

Option D is incorrect because sharing a module with an OU does not grant access to launch stacks from it. It also does not limit access to the deployment plan to only the developers who need access.