Log into Dockerhub when credentials are provided

What?
- Add 2 new optional inputs to the Github action:
  - `dockerhub-username`: the "docker ID" (aka username) for the
    Dockerhub account the action should log in as
  - `dockerhub-password`: the account password or a personal
    access token used to authorize the account login.
- Update the `./start-mongodb.sh` script to log into Dockerhub
  when these two inputs are provided.

Why?
- To allow users to authenticate with Dockerhub, and increase their
  rate limits.
  Otherwise, unauthorized requests can be rate limited, see:
  - https://www.docker.com/increase-rate-limits/
  - supercharge#62

action-types.yml

@@ -1,5 +1,9 @@
 # See https://github.com/krzema12/github-actions-typing
 inputs:
+  dockerhub-username:
+    type: string
+  dockerhub-password:
+    type: string
   mongodb-version:
     type: string
   mongodb-replica-set:

action.yml

@@ -6,6 +6,16 @@ branding:
   color: 'green'
 
 inputs:
+  dockerhub-username:
+    description: 'Docker username to use to log into Dockerhub'
+    required: false
+    default: ''
+
+  dockerhub-password:
+    description: 'Docker password or personal access token to use to log into Dockerhub'
+    required: false
+    default: ''
+
   mongodb-version:
     description: 'MongoDB version to use (default "latest")'
     required: false
@@ -45,6 +55,8 @@ runs:
   using: 'docker'
   image: 'Dockerfile'
   args:
+    - ${{ inputs.dockerhub-username }}
+    - ${{ inputs.dockerhub-password }}
     - ${{ inputs.mongodb-version }}
     - ${{ inputs.mongodb-replica-set }}
     - ${{ inputs.mongodb-port }}

start-mongodb.sh

@@ -1,13 +1,15 @@
 #!/bin/sh
 
 # Map input values from the GitHub Actions workflow to shell variables
-MONGODB_VERSION=$1
-MONGODB_REPLICA_SET=$2
-MONGODB_PORT=$3
-MONGODB_DB=$4
-MONGODB_USERNAME=$5
-MONGODB_PASSWORD=$6
-MONGODB_CONTAINER_NAME=$7
+DOCKERHUB_USERNAME=$1
+DOCKERHUB_PASSWORD=$2
+MONGODB_VERSION=$3
+MONGODB_REPLICA_SET=$4
+MONGODB_PORT=$5
+MONGODB_DB=$6
+MONGODB_USERNAME=$7
+MONGODB_PASSWORD=$8
+MONGODB_CONTAINER_NAME=$9
 
 # `mongosh` is used starting from MongoDB 5.x
 MONGODB_CLIENT="mongosh --quiet"
@@ -73,6 +75,24 @@ wait_for_mongodb () {
 #  docker rm -f $MONGODB_CONTAINER_NAME
 # fi
 
+login_to_dockerhub () {
+  echo "::group::Logging in to Docker Hub"
+  echo "Logging in as [$DOCKERHUB_USERNAME]"
+  echo ""
+
+  echo $DOCKERHUB_PASSWORD | docker login --username $DOCKERHUB_USERNAME --password-stdin
+
+  if [ $? -ne 0 ]; then
+      echo "Error logging in to Docker Hub"
+      exit 2
+  fi
+  echo "::endgroup::"
+}
+
+if [[ -n "$DOCKERHUB_USERNAME" && -n "$DOCKERHUB_PASSWORD" ]]; then
+  login_to_dockerhub
+fi
+
 
 if [ -z "$MONGODB_REPLICA_SET" ]; then
   echo "::group::Starting single-node instance, no replica set"