config: expand tilde (~) in AWS_CONFIG_FILE and AWS_SHARED_CREDENTIALS_FILE env vars

config/env_config.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/aws-sdk-go-v2/feature/ec2/imds"
+	"github.com/aws/aws-sdk-go-v2/internal/shareddefaults"
 	smithyrequestcompression "github.com/aws/smithy-go/private/requestcompression"
 )
 
@@ -340,8 +341,8 @@ func NewEnvConfig() (EnvConfig, error) {
 	setStringFromEnvVal(&cfg.Region, regionEnvKeys)
 	setStringFromEnvVal(&cfg.SharedConfigProfile, profileEnvKeys)
 
-	cfg.SharedCredentialsFile = os.Getenv(awsSharedCredentialsFileEnv)
-	cfg.SharedConfigFile = os.Getenv(awsConfigFileEnv)
+	cfg.SharedCredentialsFile = shareddefaults.ExpandHomePath(os.Getenv(awsSharedCredentialsFileEnv))
+	cfg.SharedConfigFile = shareddefaults.ExpandHomePath(os.Getenv(awsConfigFileEnv))
 
 	cfg.CustomCABundle = os.Getenv(awsCABundleEnv)
 

config/env_config_test.go

@@ -576,6 +576,17 @@ func TestNewEnvConfig(t *testing.T) {
 				AuthSchemePreference: []string{"sigv4a", "sigv4"},
 			},
 		},
+		55: {
+			Env: map[string]string{
+				"HOME":                        "/home/user",
+				"AWS_SHARED_CREDENTIALS_FILE": "~/.aws/credentials",
+				"AWS_CONFIG_FILE":             "~/.aws/config",
+			},
+			Config: EnvConfig{
+				SharedCredentialsFile: "/home/user/.aws/credentials",
+				SharedConfigFile:      "/home/user/.aws/config",
+			},
+		},
 	}
 
 	for i, c := range cases {

internal/shareddefaults/expand_home_test.go

@@ -0,0 +1,67 @@
+//go:build !windows
+// +build !windows
+
+package shareddefaults_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/internal/awstesting"
+	"github.com/aws/aws-sdk-go-v2/internal/shareddefaults"
+)
+
+func TestExpandHomePath(t *testing.T) {
+	restoreEnv := awstesting.StashEnv()
+	defer awstesting.PopEnv(restoreEnv)
+
+	os.Setenv("HOME", "/home/user")
+
+	cases := map[string]struct {
+		Input  string
+		Expect string
+	}{
+		"empty": {
+			Input:  "",
+			Expect: "",
+		},
+		"absolute path unchanged": {
+			Input:  "/absolute/path/to/config",
+			Expect: "/absolute/path/to/config",
+		},
+		"relative path unchanged": {
+			Input:  "relative/path/to/config",
+			Expect: "relative/path/to/config",
+		},
+		"tilde only": {
+			Input:  "~",
+			Expect: "/home/user",
+		},
+		"tilde with slash": {
+			Input:  "~/.aws/config",
+			Expect: filepath.Join("/home/user", ".aws", "config"),
+		},
+		"tilde with nested path": {
+			Input:  "~/projects/my app/.aws/config",
+			Expect: filepath.Join("/home/user", "projects", "my app", ".aws", "config"),
+		},
+		"tilde not at start unchanged": {
+			Input:  "/some/~/path",
+			Expect: "/some/~/path",
+		},
+		"tilde without slash unchanged": {
+			Input:  "~username/.aws/config",
+			Expect: "~username/.aws/config",
+		},
+	}
+
+	for name, c := range cases {
+		t.Run(name, func(t *testing.T) {
+			actual := shareddefaults.ExpandHomePath(c.Input)
+			if c.Expect != actual {
+				t.Errorf("expect %q, got %q", c.Expect, actual)
+			}
+		})
+	}
+}

internal/shareddefaults/shared_config.go

@@ -4,6 +4,7 @@ import (
 	"os"
 	"os/user"
 	"path/filepath"
+	"strings"
 )
 
 // SharedCredentialsFilename returns the SDK's default file path
@@ -28,6 +29,25 @@ func SharedConfigFilename() string {
 	return filepath.Join(UserHomeDir(), ".aws", "config")
 }
 
+// ExpandHomePath expands a leading ~ in the path to the user's home
+// directory. This is necessary because the Go os package does not
+// perform shell-style tilde expansion, unlike Python's
+// os.path.expanduser which is used by botocore.
+//
+// Per the AWS SDKs and Tools Reference Guide, ~ followed by / (or the
+// platform-specific path separator) at the start of a file path should
+// resolve to the home directory:
+// https://docs.aws.amazon.com/sdkref/latest/guide/file-location.html
+func ExpandHomePath(path string) string {
+	if path == "~" {
+		return UserHomeDir()
+	}
+	if strings.HasPrefix(path, "~/") || strings.HasPrefix(path, "~"+string(filepath.Separator)) {
+		return filepath.Join(UserHomeDir(), path[2:])
+	}
+	return path
+}
+
 // UserHomeDir returns the home directory for the user the process is
 // running under.
 func UserHomeDir() string {