Add support for credential_process

Fixes minio#1485

Signed-off-by: Alberto Murillo <albertomurillosilva@gmail.com>

pkg/credentials/credentials.json

@@ -0,0 +1,7 @@
+{
+    "Version": 1,
+    "SessionToken": "token",
+    "AccessKeyId": "accessKey",
+    "SecretAccessKey": "secret",
+    "Expiration": "9999-04-27T16:02:25.000Z"
+}

pkg/credentials/credentials.sample

@@ -10,3 +10,6 @@ aws_secret_access_key = secret
 [with_colon]
 aws_access_key_id: accessKey
 aws_secret_access_key: secret
+
+[with_process]
+credential_process = /bin/cat credentials.json

pkg/credentials/file_aws_credentials.go

@@ -18,18 +18,33 @@
 package credentials
 
 import (
+	"encoding/json"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"strings"
+	"time"
 
 	homedir "github.com/mitchellh/go-homedir"
 	ini "gopkg.in/ini.v1"
 )
 
+// A externalProcessCredentials stores the output of a credential_process
+type externalProcessCredentials struct {
+	Version         int
+	SessionToken    string
+	AccessKeyId     string
+	SecretAccessKey string
+	Expiration      time.Time
+}
+
 // A FileAWSCredentials retrieves credentials from the current user's home
 // directory, and keeps track if those credentials are expired.
 //
 // Profile ini file example: $HOME/.aws/credentials
 type FileAWSCredentials struct {
+	Expiry
+
 	// Path to the shared credentials file.
 	//
 	// If empty will look for "AWS_SHARED_CREDENTIALS_FILE" env variable. If the
@@ -90,6 +105,31 @@ func (p *FileAWSCredentials) Retrieve() (Value, error) {
 	// Default to empty string if not found.
 	token := iniProfile.Key("aws_session_token")
 
+	// If credential_process is defined, obtain credentials by executing
+	// the external process
+	credential_process := iniProfile.Key("credential_process").String()
+	if credential_process != "" {
+		args := strings.Fields(credential_process)
+		cmd := exec.Command(args[0], args[1:]...)
+		out, err := cmd.Output()
+		if err != nil {
+			return Value{}, err
+		}
+		var externalProcessCredentials externalProcessCredentials
+		err = json.Unmarshal([]byte(out), &externalProcessCredentials)
+		if err != nil {
+			return Value{}, err
+		}
+		p.retrieved = true
+		p.SetExpiration(externalProcessCredentials.Expiration, DefaultExpiryWindow)
+		return Value{
+			AccessKeyID:     externalProcessCredentials.AccessKeyId,
+			SecretAccessKey: externalProcessCredentials.SecretAccessKey,
+			SessionToken:    externalProcessCredentials.SessionToken,
+			SignerType:      SignatureV4,
+		}, nil
+	}
+
 	p.retrieved = true
 	return Value{
 		AccessKeyID:     id.String(),
@@ -101,7 +141,12 @@ func (p *FileAWSCredentials) Retrieve() (Value, error) {
 
 // IsExpired returns if the shared credentials have expired.
 func (p *FileAWSCredentials) IsExpired() bool {
-	return !p.retrieved
+	if p.expiration.IsZero() {
+		return !p.retrieved
+	}
+
+	now := time.Now()
+	return now.After(p.expiration)
 }
 
 // loadProfiles loads from the file pointed to by shared credentials filename for profile.

pkg/credentials/file_test.go

@@ -120,6 +120,27 @@ func TestFileAWS(t *testing.T) {
 	if !creds.IsExpired() {
 		t.Error("Should be expired if not loaded")
 	}
+
+	os.Clearenv()
+
+	creds = NewFileAWSCredentials("credentials.sample", "with_process")
+	credValues, err = creds.Get()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if credValues.AccessKeyID != "accessKey" {
+		t.Errorf("Expected 'accessKey', got %s'", credValues.AccessKeyID)
+	}
+	if credValues.SecretAccessKey != "secret" {
+		t.Errorf("Expected 'secret', got %s'", credValues.SecretAccessKey)
+	}
+	if credValues.SessionToken != "token" {
+		t.Errorf("Expected 'token', got %s'", credValues.SessionToken)
+	}
+	if creds.IsExpired() {
+		t.Error("Should not be expired")
+	}
 }
 
 func TestFileMinioClient(t *testing.T) {