cmd: support --config option

Let's support --config option by setting environment variable
DOCKER_CONFIG instead of ignoring it for docker compatibility.

Also add a test case for this change, remove the deprecated one.

This is a rework to fix:
containers#14767

Signed-off-by: Ming Liu <liu.ming50@gmail.com>

cmd/podman/root.go

@@ -400,7 +400,10 @@ func persistentPostRunE(cmd *cobra.Command, args []string) error {
 
 func configHook() {
 	if dockerConfig != "" {
-		logrus.Warn("The --config flag is ignored by Podman. Exists for Docker compatibility")
+		if err := os.Setenv("DOCKER_CONFIG", dockerConfig); err != nil {
+			fmt.Fprintf(os.Stderr, "cannot set DOCKER_CONFIG=%s: %w", dockerConfig, err)
+			os.Exit(1)
+		}
 	}
 }
 
@@ -476,8 +479,7 @@ func rootFlags(cmd *cobra.Command, podmanConfig *entities.PodmanConfig) {
 	lFlags.StringVarP(&podmanConfig.URI, "host", "H", podmanConfig.URI, "Used for Docker compatibility")
 	_ = lFlags.MarkHidden("host")
 
-	lFlags.StringVar(&dockerConfig, "config", "", "Ignored for Docker compatibility")
-	_ = lFlags.MarkHidden("config")
+	lFlags.StringVar(&dockerConfig, "config", "", "Location of config files")
 	// Context option added just for compatibility with DockerCLI.
 	lFlags.String("context", "default", "Name of the context to use to connect to the daemon (This flag is a NOOP and provided solely for scripting compatibility.)")
 	_ = lFlags.MarkHidden("context")

pkg/domain/entities/engine.go

@@ -35,7 +35,7 @@ type PodmanConfig struct {
 	ContainersConf           *config.Config
 	ContainersConfDefaultsRO *config.Config // The read-only! defaults from containers.conf.
 	DBBackend                string         // Hidden: change the database backend
-	DockerConfig             string         // Used for Docker compatibility
+	DockerConfig             string         // Location of config files
 	CgroupUsage              string         // rootless code determines Usage message
 	ConmonPath               string         // --conmon flag will set Engine.ConmonPath
 	CPUProfile               string         // Hidden: Should CPU profile be taken

test/system/001-basic.bats

@@ -35,9 +35,6 @@ function setup() {
 
     run_podman -v
     is "$output" "podman.*version \+"               "'Version line' in output"
-
-    run_podman 0+w --config foobar version
-    require_warning "The --config flag is ignored by Podman. Exists for Docker compatibility"
 }
 
 # bats test_tags=distro-integration

test/system/150-login.bats

@@ -91,6 +91,37 @@ function setup() {
     assert "$output" =~ "Error: options for paths to the credential file and to the Docker-compatible credential file can not be set simultaneously"
 }
 
+@test "podman login - check with --config option" {
+    dockerconfig=${PODMAN_LOGIN_WORKDIR}/docker
+    rm -rf $dockerconfig
+
+    registry=localhost:${PODMAN_LOGIN_REGISTRY_PORT}
+
+    run_podman login --config $dockerconfig \
+        --username ${PODMAN_LOGIN_USER} \
+        --password ${PODMAN_LOGIN_PASS} \
+        $registry
+
+    # Confirm that config file now exists
+    test -e $dockerconfig/config.json || \
+        die "podman login did not create config $dockerconfig/config.json"
+
+    # Special bracket form needed because of colon in host:port
+    run jq -r ".[\"auths\"][\"$registry\"][\"auth\"]" <$dockerconfig/config.json
+    is "$status" "0" "jq from $dockerconfig/config.json"
+
+    expect_userpass="${PODMAN_LOGIN_USER}:${PODMAN_LOGIN_PASS}"
+    actual_userpass=$(base64 -d <<<"$output")
+    is "$actual_userpass" "$expect_userpass" "credentials stored in $dockerconfig/config.json"
+
+    # Now log out and make sure credentials are removed
+    run_podman logout --config $dockerconfig $registry
+
+    run jq -r '.auths' <$dockerconfig/config.json
+    is "$status" "0" "jq from $dockerconfig/config.json"
+    is "$output" "{}" "credentials removed from $dockerconfig/config.json"
+}
+
 # Some push tests
 @test "podman push fail" {