One of our projects interacts with the client's in-house system using a SOAP API. Setting it up in the project's Dockerfile was a breeze. Here's the relevant excerpt:
dockerfile RUN apt-get update -y \ && apt-get install -y \ libxml2-dev \ php-soap \ && apt-get clean -y \ && docker-php-ext-install soap
The great thing about this is that anyone who needs to jump in on the project doesn't need to make any changes to their local dev environment; everything they need to run the project is in the Dockerfile.