use a UI wrapper to auto-decode error messages

update docs to reflect optional config

builder/amazon/common/access_config.go

@@ -19,6 +19,7 @@ import (
 type AccessConfig struct {
 	AccessKey            string `mapstructure:"access_key"`
 	CustomEndpointEc2    string `mapstructure:"custom_endpoint_ec2"`
+	DecodeAuthZMessages  bool   `mapstructure:"decode_authorization_messages"`
 	MFACode              string `mapstructure:"mfa_code"`
 	ProfileName          string `mapstructure:"profile"`
 	RawRegion            string `mapstructure:"region"`
@@ -91,6 +92,11 @@ func (c *AccessConfig) Session() (*session.Session, error) {
 		}
 		log.Printf("[INFO] AWS Auth provider used: %q", cp.ProviderName)
 	}
+
+	if c.DecodeAuthZMessages {
+		DecodeAuthZMessages(c.session)
+	}
+
 	return c.session, nil
 }
 

builder/amazon/common/errors.go

@@ -0,0 +1,58 @@
+package common
+
+import (
+	"fmt"
+	"log"
+	"regexp"
+
+	"github.com/aws/aws-sdk-go/aws/awserr"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/request"
+	"github.com/aws/aws-sdk-go/aws/session"
+	"github.com/aws/aws-sdk-go/service/sts"
+)
+
+var encodedFailureMessagePattern = regexp.MustCompile(`(?i)(.*) Encoded authorization failure message: ([\w-]+) ?( .*)?`)
+
+type stsDecoder interface {
+	DecodeAuthorizationMessage(input *sts.DecodeAuthorizationMessageInput) (*sts.DecodeAuthorizationMessageOutput, error)
+}
+
+// decodeError replaces encoded authorization messages with the
+// decoded results
+func decodeAWSError(decoder stsDecoder, err error) error {
+
+	groups := encodedFailureMessagePattern.FindStringSubmatch(err.Error())
+	if groups != nil && len(groups) > 1 {
+		result, decodeErr := decoder.DecodeAuthorizationMessage(&sts.DecodeAuthorizationMessageInput{
+			EncodedMessage: aws.String(groups[2]),
+		})
+		if decodeErr == nil {
+			msg := aws.StringValue(result.DecodedMessage)
+			return fmt.Errorf("%s Authorization failure message: '%s'%s", groups[1], msg, groups[3])
+		}
+		log.Printf("[WARN] Attempted to decode authorization message, but received: %v", decodeErr)
+	}
+	return err
+}
+
+// DecodeAuthZMessages enables automatic decoding of any
+// encoded authorization messages
+func DecodeAuthZMessages(sess *session.Session) {
+	azd := &authZMessageDecoder{
+		Decoder: sts.New(sess),
+	}
+	sess.Handlers.UnmarshalError.AfterEachFn = azd.afterEachFn
+}
+
+type authZMessageDecoder struct {
+	Decoder stsDecoder
+}
+
+func (a *authZMessageDecoder) afterEachFn(item request.HandlerListRunItem) bool {
+	if err, ok := item.Request.Error.(awserr.Error); ok && err.Code() == "UnauthorizedOperation" {
+		item.Request.Error = decodeAWSError(a.Decoder, err)
+	}
+	return true
+}

builder/amazon/common/errors_test.go

@@ -0,0 +1,70 @@
+package common
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/service/sts"
+
+	"github.com/aws/aws-sdk-go/aws/awserr"
+)
+
+type mockSTS struct {
+}
+
+func (m *mockSTS) DecodeAuthorizationMessage(input *sts.DecodeAuthorizationMessageInput) (*sts.DecodeAuthorizationMessageOutput, error) {
+	return &sts.DecodeAuthorizationMessageOutput{
+		DecodedMessage: aws.String(`{
+			"allowed": false,
+			"explicitDeny": true,
+			"matchedStatements": {}
+		}`),
+	}, nil
+}
+
+func TestErrorsParsing_RequestFailure(t *testing.T) {
+
+	ae := awserr.New("UnauthorizedOperation",
+		`You are not authorized to perform this operation. Encoded authorization failure message: D9Q7oicjOMr9l2CC-NPP1FiZXK9Ijia1k-3l0siBFCcrK3oSuMFMkBIO5TNj0HdXE-WfwnAcdycFOohfKroNO6toPJEns8RFVfy_M_IjNGmrEFJ6E62pnmBW0OLrMsXxR9FQE4gB4gJzSM0AD6cV6S3FOfqYzWBRX-sQdOT4HryGkFNRoFBr9Xbp-tRwiadwkbdHdfnV9fbRkXmnwCdULml16NBSofC4ZPepLMKmIB5rKjwk-m179UUh2XA-J5no0si6XcRo5GbHQB5QfCIwSHL4vsro2wLZUd16-8OWKyr3tVlTbQe0ERZskqRqRQ5E28QuiBCVV6XstUyo-T4lBSr75Fgnyr3wCO-dS3b_5Ns3WzA2JD4E2AJOAStXIU8IH5YuKkAg7C-dJMuBMPpmKCBEXhNoHDwCyOo5PsV3xMlc0jSb0qYGpfst_TDDtejcZfn7NssUjxVq9qkdH-OXz2gPoQB-hX8ycmZCL5UZwKc3TCLUr7TGnudHjmnMrE9cUo-yTCWfyHPLprhiYhTCKW18EikJ0O1EKI3FJ_b4F19_jFBPARjSwQc7Ut6MNCVzrPdZGYSF6acj5gPaxdy9uSkVQwWXK7Pd5MFP7EBDE1_DgYbzodgwDO2PXeVFUbSLBHKWo_ebZS9ZX2nYPcGss_sYaly0ZVSIJXp7G58B5BoFVhvVH6jYnF9XiAOjMltuP_ycu1pQP1lki500RY3baLvfeYeAsB38XZHKEgWZzq7Fei-uh89q0cjJTmlVyrfRU3q6`,
+		fmt.Errorf("You can't do it!!"))
+	rf := awserr.NewRequestFailure(ae, 400, "abc-def-123-456")
+
+	result := decodeAWSError(&mockSTS{}, rf)
+	if result == nil {
+		t.Error("Expected resulting error")
+	}
+	if !strings.Contains(result.Error(), "Authorization failure message:") {
+		t.Error("Expected authorization failure message")
+	}
+}
+
+func TestErrorsParsing_NonAuthorizationFailure(t *testing.T) {
+
+	ae := awserr.New("BadRequest",
+		`You did something wrong. Try again`,
+		fmt.Errorf("Request was no good."))
+	rf := awserr.NewRequestFailure(ae, 400, "abc-def-123-456")
+
+	result := decodeAWSError(&mockSTS{}, rf)
+	if result == nil {
+		t.Error("Expected resulting error")
+	}
+	if result != rf {
+		t.Error("Expected original error to be returned unchanged")
+	}
+}
+
+func TestErrorsParsing_NonAWSError(t *testing.T) {
+
+	err := fmt.Errorf("Random error occurred")
+
+	result := decodeAWSError(&mockSTS{}, err)
+	if result == nil {
+		t.Error("Expected resulting error")
+	}
+	if result != err {
+		t.Error("Expected original error to be returned unchanged")
+	}
+}

website/source/docs/builders/amazon-chroot.html.md

@@ -121,6 +121,11 @@ each category, the available configuration keys are alphabetized.
     provider whose API is compatible with aws EC2. Specify another endpoint
     like this `https://ec2.custom.endpoint.com`.
 
+-   `decode_authorization_messages` (boolean) - Enable automatic decoding of any
+    encoded authorization (error) messages using the `sts:DecodeAuthorizationMessage` API.
+    Note: requires that the effective user/role have permissions to `sts:DecodeAuthorizationMessage`
+    on resource `*`. Default `false`.
+
 -   `device_path` (string) - The path to the device where the root volume of the
     source AMI will be attached. This defaults to "" (empty string), which
     forces Packer to find an open device automatically.

website/source/docs/builders/amazon-ebs.html.md

@@ -151,6 +151,11 @@ builder.
     provider whose API is compatible with aws EC2. Specify another endpoint
     like this `https://ec2.custom.endpoint.com`.
 
+-   `decode_authorization_messages` (boolean) - Enable automatic decoding of any
+    encoded authorization (error) messages using the `sts:DecodeAuthorizationMessage` API.
+    Note: requires that the effective user/role have permissions to `sts:DecodeAuthorizationMessage`
+    on resource `*`. Default `false`.
+
 -   `disable_stop_instance` (boolean) - Packer normally stops the build instance
     after all provisioners have run. For Windows instances, it is sometimes
     desirable to [run Sysprep](http://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/ami-create-standard.html)

website/source/docs/builders/amazon-ebssurrogate.html.md

@@ -144,6 +144,11 @@ builder.
     provider whose API is compatible with aws EC2. Specify another endpoint
     like this `https://ec2.custom.endpoint.com`.
 
+-   `decode_authorization_messages` (boolean) - Enable automatic decoding of any
+    encoded authorization (error) messages using the `sts:DecodeAuthorizationMessage` API.
+    Note: requires that the effective user/role have permissions to `sts:DecodeAuthorizationMessage`
+    on resource `*`. Default `false`.
+
 -   `disable_stop_instance` (boolean) - Packer normally stops the build instance
     after all provisioners have run. For Windows instances, it is sometimes
     desirable to [run Sysprep](http://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/ami-create-standard.html)

website/source/docs/builders/amazon-ebsvolume.html.md

@@ -137,6 +137,11 @@ builder.
     }
     ```
 
+-   `decode_authorization_messages` (boolean) - Enable automatic decoding of any
+    encoded authorization (error) messages using the `sts:DecodeAuthorizationMessage` API.
+    Note: requires that the effective user/role have permissions to `sts:DecodeAuthorizationMessage`
+    on resource `*`. Default `false`.
+
 -   `ebs_optimized` (boolean) - Mark instance as [EBS
     Optimized](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSOptimized.html).
     Default `false`.

website/source/docs/builders/amazon-instance.html.md

@@ -189,6 +189,11 @@ builder.
     provider whose API is compatible with aws EC2. Specify another endpoint
     like this `https://ec2.custom.endpoint.com`.
 
+-   `decode_authorization_messages` (boolean) - Enable automatic decoding of any
+    encoded authorization (error) messages using the `sts:DecodeAuthorizationMessage` API.
+    Note: requires that the effective user/role have permissions to `sts:DecodeAuthorizationMessage`
+    on resource `*`. Default `false`.
+
 -   `ebs_optimized` (boolean) - Mark instance as [EBS
     Optimized](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSOptimized.html).
     Default `false`.