Add secrets support

Signed-off-by: Jason Dictos <jdictos@een.com>

Author: JasonDictos

README.md

@@ -208,6 +208,22 @@ version is the image's digest.
   { "EMAIL": "me@yopmail.com", "HOW_MANY_THINGS": 1, "DO_THING": false }
   ```
 
+* `secrets`: *Optional.* A map of Docker build-time secrets. These will be
+  available as mounted paths only during the docker build phase.
+  
+  Secrets are not stored in any metadata or layers, so they are safe to use for
+  access tokens and the like during the build.
+
+  Example:
+
+  ```yaml
+  secrets:
+    secret1: 
+      env: BUILD_ID
+    secret2:
+      source: /a/secret/file.txt
+  ```
+
 * `cache`: *Optional.* Default `false`. When the `build` parameter is set,
   first pull `image:tag` from the Docker registry (so as to use cached
   intermediate images when building). This will cause the resource to fail

assets/out

@@ -78,6 +78,7 @@ tag_prefix=$(jq -r '.params.tag_prefix // ""' < $payload)
 additional_tags=$(jq -r '.params.additional_tags // ""' < $payload)
 need_tag_as_latest=$(jq -r '.params.tag_as_latest // "false"' < $payload)
 build_args=$(jq -r '.params.build_args // {}' < $payload)
+secrets=$(jq -r '.params.secrets // {}' < $payload)
 build_args_file=$(jq -r '.params.build_args_file // ""' < $payload)
 labels=$(jq -r '.params.labels // {}' < $payload)
 labels_file=$(jq -r '.params.labels_file // ""' < $payload)
@@ -215,6 +216,32 @@ elif [ -n "$build" ]; then
     fi
   fi
 
+  expanded_secrets=()
+
+  secret_keys=($(echo "$secrets" | jq -r 'keys | join(" ")'))
+  if [ "${#secret_keys[@]}" -gt 0 ]; then
+    # Force buildkit on
+    export DOCKER_BUILDKIT=1
+    for key in "${secret_keys[@]}"; do
+      value=$(echo "$secrets" | jq -r --arg "k" "$key" '.[$k]')
+      for var in BUILD_ID BUILD_NAME BUILD_JOB_NAME BUILD_PIPELINE_NAME BUILD_TEAM_NAME ATC_EXTERNAL_URL; do
+        value="${value//\$$var/${!var:-}}"
+        value="${value//\$\{$var\}/${!var:-}}"
+      done
+      secret="id=${key}"
+      sub=$(jq -r ".params.secrets.${key} // {}" < $payload)
+      sub_keys=($(echo "$sub" | jq -r 'keys | join(" ")'))
+      if [ "${#sub_keys[@]}" -gt 0 ]; then
+        expanded_secrets+=("--secret")
+        for key in "${sub_keys[@]}"; do
+          value=$(echo "$sub" | jq -r --arg "k" "$key" '.[$k]')
+          secret="${secret},${key}=${value}"
+        done
+        expanded_secrets+=("${secret}")
+      fi
+    done
+  fi
+
   expanded_labels=()
 
   label_keys=($(echo "$labels" | jq -r 'keys | join(" ")'))
@@ -261,7 +288,7 @@ elif [ -n "$build" ]; then
   # NOTE: deactivate amazon-ecr-credential-helper so that builds go through with the DOCKER_BUILDKIT set
   cp ~/.docker/config.json ~/.docker/config.json.bak
   cat <<< "$(jq 'del(.credsStore)' ~/.docker/config.json)" > ~/.docker/config.json
-  docker build -t "${repository}:${tag_name}" "${target[@]}" "${expanded_build_args[@]}" "${expanded_labels[@]}" "${ssh_args[@]}" -f "$dockerfile" $cache_from "$build"
+  docker build -t "${repository}:${tag_name}" "${target[@]}" "${expanded_build_args[@]}" "${expanded_secrets[@]}" "${expanded_labels[@]}" "${ssh_args[@]}" -f "$dockerfile" $cache_from "$build"
   mv ~/.docker/config.json.bak ~/.docker/config.json # This restores the credsStore: ecr-login to config.json if needed
 
 elif [ -n "$load_file" ]; then

tests/out_test.go

@@ -133,6 +133,37 @@ var _ = Describe("Out", func() {
 		})
 	})
 
+	Context("when secrets are provided", func() {
+		It("passes the arguments correctly to the docker daemon", func() {
+			session := put(map[string]interface{}{
+				"source": map[string]interface{}{
+					"repository": "test",
+				},
+				"params": map[string]interface{}{
+					"build": "/docker-image-resource/tests/fixtures/build",
+					"secrets": map[string]interface{}{
+						"secret1": map[string]interface{}{
+              "env": "GITHUB_TOKEN",
+            },
+						"secret2": map[string]interface{}{
+              "source": "/a/file/path.txt",
+            },
+						"secret3": map[string]interface{}{
+              "source": "/a/file/path with a space in it.txt",
+            },
+					},
+				},
+			})
+
+			Expect(session.Err).To(gbytes.Say(dockerarg(`--secret`)))
+			Expect(session.Err).To(gbytes.Say(dockerarg(`id=secret1,env=GITHUB_TOKEN`)))
+			Expect(session.Err).To(gbytes.Say(dockerarg(`--secret`)))
+			Expect(session.Err).To(gbytes.Say(dockerarg(`id=secret2,source=/a/file/path.txt`)))
+			Expect(session.Err).To(gbytes.Say(dockerarg(`--secret`)))
+			Expect(session.Err).To(gbytes.Say(dockerarg(`id=secret3,source=/a/file/path with a space in it.txt`)))
+		})
+	})
+
 	Context("when labels are provided", func() {
 		It("passes the labels correctly to the docker daemon", func() {
 			session := put(map[string]interface{}{