[login] allow sourcing STS credentials from environment (closes #861)

USAGE.md

@@ -304,6 +304,14 @@ You can use the `aws-vault login` command to open a browser window and login to
 $ aws-vault login work
 ```
 
+If you have temporary STS credentials already available in your environment, you can have aws-vault use these credentials to sign you in.
+This is useful when you had to use something else than aws-vault to retrieve temporary credentials:
+
+```shell
+# AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, and AWS_SESSION_TOKEN must be set in your environment prior to running the below
+$ aws-vault login
+```
+
 ### Removing stored sessions
 
 If you want to remove sessions managed by `aws-vault` before they expire, you can do this with `aws-vault clear` command.

cli/login.go

@@ -55,7 +55,6 @@ func ConfigureLoginCommand(app *kingpin.Application, a *AwsVault) {
 		BoolVar(&input.UseStdout)
 
 	cmd.Arg("profile", "Name of the profile").
-		Required().
 		HintAction(a.MustGetProfileNames).
 		StringVar(&input.ProfileName)
 
@@ -94,22 +93,34 @@ func LoginCommand(input LoginCommandInput, f *vault.ConfigFile, keyring keyring.
 
 	var credsProvider aws.CredentialsProvider
 
-	ckr := &vault.CredentialKeyring{Keyring: keyring}
-	// If AssumeRole or sso.GetRoleCredentials isn't used, GetFederationToken has to be used for IAM credentials
-	if config.HasRole() || config.HasSSOStartURL() {
-		credsProvider, err = vault.NewTempCredentialsProvider(config, ckr)
+	if input.ProfileName == "" {
+		// When no profile is specified, source credentials from the environment
+		credsProvider = vault.NewEnvironmentCredentialsProvider()
 	} else {
-		credsProvider, err = vault.NewFederationTokenCredentialsProvider(input.ProfileName, ckr, config)
-	}
-	if err != nil {
-		return fmt.Errorf("profile %s: %w", input.ProfileName, err)
+		// Use a profile from the AWS config file
+		ckr := &vault.CredentialKeyring{Keyring: keyring}
+		if config.HasRole() || config.HasSSOStartURL() {
+			// If AssumeRole or sso.GetRoleCredentials isn't used, GetFederationToken has to be used for IAM credentials
+			credsProvider, err = vault.NewTempCredentialsProvider(config, ckr)
+		} else {
+			credsProvider, err = vault.NewFederationTokenCredentialsProvider(input.ProfileName, ckr, config)
+		}
+		if err != nil {
+			return fmt.Errorf("profile %s: %w", input.ProfileName, err)
+		}
 	}
 
 	creds, err := credsProvider.Retrieve(context.TODO())
 	if err != nil {
-		return fmt.Errorf("Failed to get credentials for %s: %w", config.ProfileName, err)
+		return fmt.Errorf("Failed to get credentials: %w", err)
+	}
+	if creds.SessionToken == "" {
+		// When sourcing credentials from the environment, it's possible a session token wasn't set
+		// Generating a sign-in link requires temporary credentials, so we return an error
+		// NOTE: We deliberately chose to have this logic here rather than in 'EnvironmentVariablesCredentialsProvider'
+		// to make it possible to reuse it for other commands than `aws-vault login` in the future
+		return fmt.Errorf("failed to retrieve a session token. Cannot generate a login URL without it")
 	}
-
 	jsonBytes, err := json.Marshal(map[string]string{
 		"sessionId":    creds.AccessKeyID,
 		"sessionKey":   creds.SecretAccessKey,

go.mod

@@ -6,6 +6,7 @@ require (
 	github.com/99designs/keyring v1.2.0
 	github.com/alecthomas/kingpin v0.0.0-20200323085623-b6657d9477a6
 	github.com/aws/aws-sdk-go-v2 v1.14.0
+	github.com/aws/aws-sdk-go-v2/config v1.14.0
 	github.com/aws/aws-sdk-go-v2/service/iam v1.17.0
 	github.com/aws/aws-sdk-go-v2/service/sso v1.10.0
 	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.11.0
@@ -22,8 +23,11 @@ require (
 	github.com/99designs/go-keychain v0.0.0-20191008050251-8e49817e8af4 // indirect
 	github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751 // indirect
 	github.com/alecthomas/units v0.0.0-20211218093645-b94a6e3cc137 // indirect
+	github.com/aws/aws-sdk-go-v2/credentials v1.9.0 // indirect
+	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.11.0 // indirect
 	github.com/aws/aws-sdk-go-v2/internal/configsources v1.1.5 // indirect
 	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.3.0 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/ini v1.3.6 // indirect
 	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.8.0 // indirect
 	github.com/aws/smithy-go v1.11.0 // indirect
 	github.com/danieljoos/wincred v1.1.2 // indirect

go.sum

@@ -12,10 +12,18 @@ github.com/alecthomas/units v0.0.0-20211218093645-b94a6e3cc137 h1:s6gZFSlWYmbqAu
 github.com/alecthomas/units v0.0.0-20211218093645-b94a6e3cc137/go.mod h1:OMCwj8VM1Kc9e19TLln2VL61YJF0x1XFtfdL4JdbSyE=
 github.com/aws/aws-sdk-go-v2 v1.14.0 h1:IzSYBJHu0ZdUi27kIW6xVrs0eSxI4AzwbenzfXhhVs4=
 github.com/aws/aws-sdk-go-v2 v1.14.0/go.mod h1:ZA3Y8V0LrlWj63MQAnRHgKf/5QB//LSZCPNWlWrNGLU=
+github.com/aws/aws-sdk-go-v2/config v1.14.0 h1:Yr8/7R6H8nqqfqgLATrcB83ax6FE2HcDXEB54XPhE98=
+github.com/aws/aws-sdk-go-v2/config v1.14.0/go.mod h1:GKDRrvsq/PTaOYc9252u8Uah1hsIdtor4oIrFvUNPNM=
+github.com/aws/aws-sdk-go-v2/credentials v1.9.0 h1:R3Q5s1uGLUg0aUzi+oRaUqRXhd17G/9+PiVnAwXp4sY=
+github.com/aws/aws-sdk-go-v2/credentials v1.9.0/go.mod h1:PyHKqk/+tJuDY7T8R580S1j/AcSD+ODeUZ99CAUKLqQ=
+github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.11.0 h1:CkM4d3lNeMXMZ0BDX3BtCktnKA1Ftud84Hb6d+Ix4Rk=
+github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.11.0/go.mod h1:rwdUKJV5rm+vHu1ncD1iGDqahBEL8O0tBjVqo9eO2N0=
 github.com/aws/aws-sdk-go-v2/internal/configsources v1.1.5 h1:+phazLmKkjBYhFTsGYH9J7jgnA8+Aer2yE4QeS4zn6A=
 github.com/aws/aws-sdk-go-v2/internal/configsources v1.1.5/go.mod h1:2hXc8ooJqF2nAznsbJQIn+7h851/bu8GVC80OVTTqf8=
 github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.3.0 h1:PO+HNeJBeRK0yVD9CQZ+VUrYfd5sXqS7YdPYHHcDkR4=
 github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.3.0/go.mod h1:miRSv9l093jX/t/j+mBCaLqFHo9xKYzJ7DGm1BsGoJM=
+github.com/aws/aws-sdk-go-v2/internal/ini v1.3.6 h1:c8s9EhIPVFMFS+R1+rtEghGrf7v83gSUWbcCYX/OPes=
+github.com/aws/aws-sdk-go-v2/internal/ini v1.3.6/go.mod h1:o1ippSg3yJx5EuT4AOGXJCUcmt5vrcxla1cg6K1Q8Iw=
 github.com/aws/aws-sdk-go-v2/service/iam v1.17.0 h1:lG9Hx7BGOiVFTS0qJ0nM//yCxvGNxoqzfOSvo2dpsl0=
 github.com/aws/aws-sdk-go-v2/service/iam v1.17.0/go.mod h1:1o13iK9CH2OanAQZpbxKdhGj23ij4V8ZZ9DFnSve3fc=
 github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.8.0 h1:JNMALY8/ZnFsfAzBHtC4gq8JeZPANmIoI2VaBgYzbf8=

vault/environmentvariablescredentialsprovider.go

@@ -0,0 +1,21 @@
+package vault
+
+import (
+	"context"
+	"fmt"
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/config"
+)
+
+// EnvironmentVariablesCredentialsProvider retrieves AWS credentials available in the OS environment variables
+type EnvironmentVariablesCredentialsProvider struct {
+}
+
+func (m *EnvironmentVariablesCredentialsProvider) Retrieve(context.Context) (aws.Credentials, error) {
+	configFromEnv, err := config.NewEnvConfig()
+	if err != nil {
+		err := fmt.Errorf("unable to authenticate to AWS through your environment variables: %w", err)
+		return aws.Credentials{}, err
+	}
+	return configFromEnv.Credentials, nil
+}

vault/vault.go

@@ -291,6 +291,10 @@ func NewFederationTokenCredentialsProvider(profileName string, k *CredentialKeyr
 	}, nil
 }
 
+func NewEnvironmentCredentialsProvider() aws.CredentialsProvider {
+	return &EnvironmentVariablesCredentialsProvider{}
+}
+
 func FindMasterCredentialsNameFor(profileName string, keyring *CredentialKeyring, config *Config) (string, error) {
 	hasMasterCreds, err := keyring.Has(profileName)
 	if err != nil {