Add mfa_process config

USAGE.md

@@ -7,6 +7,7 @@
       - [`include_profile`](#include_profile)
       - [`session_tags` and `transitive_session_tags`](#session_tags-and-transitive_session_tags)
       - [`source_identity`](#source_identity)
+      - [`mfa_process`](#mfa_process)
     - [Environment variables](#environment-variables)
   - [Backends](#backends)
     - [Keychain](#keychain)
@@ -26,9 +27,11 @@
     - [Temporary credentials limitations with STS, IAM](#temporary-credentials-limitations-with-sts-iam)
   - [MFA](#mfa)
     - [Gotchas with MFA config](#gotchas-with-mfa-config)
-  - [Single sign on with AWS IAM Identity Center (formerly AWS SSO)](#aws-single-sign-on-aws-sso)
+  - [Single Sign On (SSO)](#single-sign-on-sso)
   - [Assuming roles with web identities](#assuming-roles-with-web-identities)
   - [Using `credential_process`](#using-credential_process)
+    - [Invoking `aws-vault` via `credential_process`](#invoking-aws-vault-via-credential_process)
+    - [Invoking `credential_process` via `aws-vault`](#invoking-credential_process-via-aws-vault)
   - [Using a Yubikey](#using-a-yubikey)
     - [Prerequisites](#prerequisites)
     - [Setup](#setup)
@@ -135,6 +138,26 @@ role_arn=arn:aws:iam::123456789:role/developers
 source_identity=your_user_name
 ```
 
+#### `mfa_process`
+If you have a method to generate an MFA token, you can use it with `aws-vault` by specifying the `mfa_process` option in a profile of your `~/.aws/config` file. The value of `mfa_process` should be a command that will output the MFA token to stdout.
+
+For example, to use `pass` to retrieve an MFA token from a password store entry, you could use the following:
+
+```ini
+[profile foo]
+mfa_serial=arn:aws:iam::123456789:mfa/johnsmith
+mfa_process=pass otp my_aws_mfa
+```
+
+Or another example using 1Password
+
+```ini
+[profile foo]
+mfa_serial=arn:aws:iam::123456789:mfa/johnsmith
+mfa_process=op item get my_aws_mfa --otp
+```
+
+WARNING: Use of this option runs against security best practices. It is recommended that you use a dedicated MFA device.
 
 ### Environment variables
 
@@ -429,7 +452,7 @@ role_arn = arn:aws:iam::33333333333:role/role2
 include_profile = jon
 ```
 
-## AWS Single Sign-On (AWS SSO)
+## Single Sign On (SSO)
 
 _AWS IAM Identity Center provides single sign on, and was previously known as AWS SSO._
 

prompt/kdialog.go

@@ -17,5 +17,7 @@ func KDialogMfaPrompt(mfaSerial string) (string, error) {
 }
 
 func init() {
-	Methods["kdialog"] = KDialogMfaPrompt
+	if _, err := exec.LookPath("kdialog"); err == nil {
+		Methods["kdialog"] = KDialogMfaPrompt
+	}
 }

prompt/osascript.go

@@ -22,5 +22,7 @@ func OSAScriptMfaPrompt(mfaSerial string) (string, error) {
 }
 
 func init() {
-	Methods["osascript"] = OSAScriptMfaPrompt
+	if _, err := exec.LookPath("osascript"); err == nil {
+		Methods["osascript"] = OSAScriptMfaPrompt
+	}
 }

prompt/ykman.go

@@ -46,5 +46,7 @@ func YkmanMfaProvider(mfaSerial string) (string, error) {
 }
 
 func init() {
-	Methods["ykman"] = YkmanMfaProvider
+	if _, err := exec.LookPath("ykman"); err == nil {
+		Methods["ykman"] = YkmanMfaProvider
+	}
 }

prompt/zenity.go

@@ -17,5 +17,7 @@ func ZenityMfaPrompt(mfaSerial string) (string, error) {
 }
 
 func init() {
-	Methods["zenity"] = ZenityMfaPrompt
+	if _, err := exec.LookPath("zenity"); err == nil {
+		Methods["zenity"] = ZenityMfaPrompt
+	}
 }

vault/assumeroleprovider.go

@@ -21,7 +21,7 @@ type AssumeRoleProvider struct {
 	Tags              map[string]string
 	TransitiveTagKeys []string
 	SourceIdentity    string
-	Mfa
+	*Mfa
 }
 
 // Retrieve generates a new set of temporary credentials using STS AssumeRole
@@ -62,8 +62,8 @@ func (p *AssumeRoleProvider) assumeRole(ctx context.Context) (*ststypes.Credenti
 		input.ExternalId = aws.String(p.ExternalID)
 	}
 
-	if p.MfaSerial != "" {
-		input.SerialNumber = aws.String(p.MfaSerial)
+	if p.GetMfaSerial() != "" {
+		input.SerialNumber = aws.String(p.GetMfaSerial())
 		input.TokenCode, err = p.GetMfaToken()
 		if err != nil {
 			return nil, err

vault/config.go

@@ -149,6 +149,7 @@ type ProfileSection struct {
 	TransitiveSessionTags   string `ini:"transitive_session_tags,omitempty"`
 	SourceIdentity          string `ini:"source_identity,omitempty"`
 	CredentialProcess       string `ini:"credential_process,omitempty"`
+	MfaProcess              string `ini:"mfa_process,omitempty"`
 }
 
 // SSOSessionSection is a [sso-session] section of the config file
@@ -379,6 +380,9 @@ func (cl *ConfigLoader) populateFromConfigFile(config *Config, profileName strin
 	if config.CredentialProcess == "" {
 		config.CredentialProcess = psection.CredentialProcess
 	}
+	if config.MfaProcess == "" {
+		config.MfaProcess = psection.MfaProcess
+	}
 	if sessionTags := psection.SessionTags; sessionTags != "" && config.SessionTags == nil {
 		err := config.SetSessionTags(sessionTags)
 		if err != nil {
@@ -559,6 +563,9 @@ type Config struct {
 	MfaToken        string
 	MfaPromptMethod string
 
+	// MfaProcess specifies external command to run to get an MFA token
+	MfaProcess string
+
 	// AssumeRole config
 	RoleARN         string
 	RoleSessionName string

vault/mfa.go

@@ -0,0 +1,64 @@
+package vault
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/99designs/aws-vault/v7/prompt"
+	"github.com/aws/aws-sdk-go-v2/aws"
+)
+
+// Mfa contains options for an MFA device
+type Mfa struct {
+	mfaSerial     string
+	mfaPromptFunc prompt.Func
+}
+
+// GetMfaToken returns the MFA token
+func (m *Mfa) GetMfaToken() (*string, error) {
+	if m.mfaPromptFunc != nil {
+		token, err := m.mfaPromptFunc(m.mfaSerial)
+		return aws.String(token), err
+	}
+
+	return nil, errors.New("No prompt found")
+}
+
+// GetMfaSerial returns the MFA serial
+func (m *Mfa) GetMfaSerial() string {
+	return m.mfaSerial
+}
+
+func NewMfa(config *Config) *Mfa {
+	m := Mfa{
+		mfaSerial: config.MfaSerial,
+	}
+	if config.MfaToken != "" {
+		m.mfaPromptFunc = func(_ string) (string, error) { return config.MfaToken, nil }
+	} else if config.MfaProcess != "" {
+		m.mfaPromptFunc = func(_ string) (string, error) {
+			log.Println("Executing mfa_process")
+			return ProcessMfaProvider(config.MfaProcess)
+		}
+	} else {
+		m.mfaPromptFunc = prompt.Method(config.MfaPromptMethod)
+	}
+
+	return &m
+}
+
+func ProcessMfaProvider(processCmd string) (string, error) {
+	cmd := exec.Command("/bin/sh", "-c", processCmd)
+	cmd.Stderr = os.Stderr
+
+	out, err := cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("process provider: %w", err)
+	}
+
+	return strings.TrimSpace(string(out)), nil
+}

vault/sessiontokenprovider.go

@@ -14,7 +14,7 @@ import (
 type SessionTokenProvider struct {
 	StsClient *sts.Client
 	Duration  time.Duration
-	Mfa
+	*Mfa
 }
 
 // Retrieve generates a new set of temporary credentials using STS GetSessionToken
@@ -41,8 +41,8 @@ func (p *SessionTokenProvider) GetSessionToken(ctx context.Context) (*ststypes.C
 		DurationSeconds: aws.Int32(int32(p.Duration.Seconds())),
 	}
 
-	if p.MfaSerial != "" {
-		input.SerialNumber = aws.String(p.MfaSerial)
+	if p.GetMfaSerial() != "" {
+		input.SerialNumber = aws.String(p.GetMfaSerial())
 		input.TokenCode, err = p.GetMfaToken()
 		if err != nil {
 			return nil, err

vault/vault.go

@@ -2,13 +2,11 @@ package vault
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"log"
 	"os"
 	"time"
 
-	"github.com/99designs/aws-vault/v7/prompt"
 	"github.com/99designs/keyring"
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/aws-sdk-go-v2/service/sso"
@@ -45,28 +43,6 @@ func FormatKeyForDisplay(k string) string {
 	return fmt.Sprintf("****************%s", k[len(k)-4:])
 }
 
-// Mfa contains options for an MFA device
-type Mfa struct {
-	MfaToken        string
-	MfaPromptMethod string
-	MfaSerial       string
-}
-
-// GetMfaToken returns the MFA token
-func (m *Mfa) GetMfaToken() (*string, error) {
-	if m.MfaToken != "" {
-		return aws.String(m.MfaToken), nil
-	}
-
-	if m.MfaPromptMethod != "" {
-		promptFunc := prompt.Method(m.MfaPromptMethod)
-		token, err := promptFunc(m.MfaSerial)
-		return aws.String(token), err
-	}
-
-	return nil, errors.New("No prompt found")
-}
-
 // NewMasterCredentialsProvider creates a provider for the master credentials
 func NewMasterCredentialsProvider(k *CredentialKeyring, credentialsName string) *KeyringProvider {
 	return &KeyringProvider{k, credentialsName}
@@ -78,11 +54,7 @@ func NewSessionTokenProvider(credsProvider aws.CredentialsProvider, k keyring.Ke
 	sessionTokenProvider := &SessionTokenProvider{
 		StsClient: sts.NewFromConfig(cfg),
 		Duration:  config.GetSessionTokenDuration(),
-		Mfa: Mfa{
-			MfaToken:        config.MfaToken,
-			MfaPromptMethod: config.MfaPromptMethod,
-			MfaSerial:       config.MfaSerial,
-		},
+		Mfa:       NewMfa(config),
 	}
 
 	if UseSessionCache {
@@ -114,11 +86,7 @@ func NewAssumeRoleProvider(credsProvider aws.CredentialsProvider, k keyring.Keyr
 		Tags:              config.SessionTags,
 		TransitiveTagKeys: config.TransitiveSessionTags,
 		SourceIdentity:    config.SourceIdentity,
-		Mfa: Mfa{
-			MfaSerial:       config.MfaSerial,
-			MfaToken:        config.MfaToken,
-			MfaPromptMethod: config.MfaPromptMethod,
-		},
+		Mfa:               NewMfa(config),
 	}
 
 	if UseSessionCache && config.MfaSerial != "" {