config: Add support for SharedConfig file ca_bundle parameter

Adds support for the `ca_bundle` parameter in shared config and
credentials files. The usage of the file is the same as environment
variable, `AWS_CA_BUNDLE`, but sourced from shared config.

Fixes aws#1589

Usage:
  [profile myProfile]
  ca_bundle = path/to/ca/bundle.pem

config/codegen/main.go

@@ -22,7 +22,7 @@ const (
 var implAsserts = map[string][]string{
 	"sharedConfigProfileProvider":              {envConfigType, loadOptionsType},
 	"sharedConfigFilesProvider":                {envConfigType, loadOptionsType},
-	"customCABundleProvider":                   {envConfigType, loadOptionsType},
+	"customCABundleProvider":                   {envConfigType, sharedConfigType, loadOptionsType},
 	"regionProvider":                           {envConfigType, sharedConfigType, loadOptionsType, ec2IMDSRegionType},
 	"credentialsProviderProvider":              {loadOptionsType},
 	"defaultRegionProvider":                    {loadOptionsType},

config/shared_config.go

@@ -1,9 +1,12 @@
 package config
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -81,6 +84,8 @@ const (
 	// Retry options
 	retryMaxAttemptsKey = "max_attempts"
 	retryModeKey        = "retry_mode"
+
+	caBundleKey = "ca_bundle"
 )
 
 // defaultSharedConfigProfile allows for swapping the default profile for testing
@@ -171,12 +176,14 @@ type SharedConfig struct {
 	// s3_use_arn_region=true
 	S3UseARNRegion *bool
 
-	// Specifies the EC2 Instance Metadata Service default endpoint selection mode (IPv4 or IPv6)
+	// Specifies the EC2 Instance Metadata Service default endpoint selection
+	// mode (IPv4 or IPv6)
 	//
 	// ec2_metadata_service_endpoint_mode=IPv6
 	EC2IMDSEndpointMode imds.EndpointModeState
 
-	// Specifies the EC2 Instance Metadata Service endpoint to use. If specified it overrides EC2IMDSEndpointMode.
+	// Specifies the EC2 Instance Metadata Service endpoint to use. If
+	// specified it overrides EC2IMDSEndpointMode.
 	//
 	// ec2_metadata_service_endpoint=http://fd00:ec2::254
 	EC2IMDSEndpoint string
@@ -214,6 +221,22 @@ type SharedConfig struct {
 	//
 	// retry_mode=standard
 	RetryMode aws.RetryMode
+
+	// Sets the path to a custom Credentials Authority (CA) Bundle PEM file
+	// that the SDK will use instead of the system's root CA bundle. Only use
+	// this if you want to configure the SDK to use a custom set of CAs.
+	//
+	// Enabling this option will attempt to merge the Transport into the SDK's
+	// HTTP client. If the client's Transport is not a http.Transport an error
+	// will be returned. If the Transport's TLS config is set this option will
+	// cause the SDK to overwrite the Transport's TLS config's  RootCAs value.
+	//
+	// Setting a custom HTTPClient in the aws.Config options will override this
+	// setting. To use this option and custom HTTP client, the HTTP client
+	// needs to be provided when creating the config. Not the service client.
+	//
+	//  ca_bundle=$HOME/my_custom_ca_bundle
+	CustomCABundle string
 }
 
 func (c SharedConfig) getDefaultsMode(ctx context.Context) (value aws.DefaultsMode, ok bool, err error) {
@@ -323,6 +346,19 @@ func (c SharedConfig) GetUseFIPSEndpoint(ctx context.Context) (value aws.FIPSEnd
 	return c.UseFIPSEndpoint, true, nil
 }
 
+// GetCustomCABundle returns the custom CA bundle's PEM bytes if the file was
+func (c SharedConfig) getCustomCABundle(context.Context) (io.Reader, bool, error) {
+	if len(c.CustomCABundle) == 0 {
+		return nil, false, nil
+	}
+
+	b, err := ioutil.ReadFile(c.CustomCABundle)
+	if err != nil {
+		return nil, false, err
+	}
+	return bytes.NewReader(b), true, nil
+}
+
 // loadSharedConfigIgnoreNotExist is an alias for loadSharedConfig with the
 // addition of ignoring when none of the files exist or when the profile
 // is not found in any of the files.
@@ -871,6 +907,8 @@ func (c *SharedConfig) setFromIniSection(profile string, section ini.Section) er
 		return fmt.Errorf("failed to load %s from shared config, %w", retryModeKey, err)
 	}
 
+	updateString(&c.CustomCABundle, section, caBundleKey)
+
 	// Shared Credentials
 	creds := aws.Credentials{
 		AccessKeyID:     section.String(accessKeyIDKey),

config/shared_config_test.go

@@ -574,6 +574,15 @@ func TestNewSharedConfig(t *testing.T) {
 			Profile:              "retrywithinvalidattempts",
 			Err:                  fmt.Errorf("failed to load max_attempts from shared config, invalid value max_attempts=invalid, expect integer"),
 		},
+		"ca bundle options": {
+			ConfigFilenames:      []string{testConfigFilename},
+			CredentialsFilenames: []string{testCredentialsFilename},
+			Profile:              "with_ca_bundle",
+			Expected: SharedConfig{
+				Profile:        "with_ca_bundle",
+				CustomCABundle: "custom_ca_bundle_file.pem",
+			},
+		},
 		"merged profiles across files": {
 			ConfigFilenames:      []string{testConfigFilename},
 			CredentialsFilenames: []string{testCredentialsFilename},

config/testdata/shared_config

@@ -257,3 +257,6 @@ retry_mode = invalid
 
 [profile retrywithinvalidattempts]
 max_attempts = invalid
+
+[profile with_ca_bundle]
+ca_bundle = custom_ca_bundle_file.pem