s3: The ability to specify an IAM role for cross-account interaction

backend/s3/s3.go

@@ -30,9 +30,11 @@ import (
 	v4signer "github.com/aws/aws-sdk-go-v2/aws/signer/v4"
 	awsconfig "github.com/aws/aws-sdk-go-v2/config"
 	"github.com/aws/aws-sdk-go-v2/credentials"
+	"github.com/aws/aws-sdk-go-v2/credentials/stscreds"
 	"github.com/aws/aws-sdk-go-v2/feature/s3/manager"
 	"github.com/aws/aws-sdk-go-v2/service/s3"
 	"github.com/aws/aws-sdk-go-v2/service/s3/types"
+	"github.com/aws/aws-sdk-go-v2/service/sts"
 	"github.com/aws/smithy-go"
 	"github.com/aws/smithy-go/logging"
 	"github.com/aws/smithy-go/middleware"
@@ -325,6 +327,30 @@ If empty it will default to the environment variable "AWS_PROFILE" or
 			Help:      "An AWS session token.",
 			Advanced:  true,
 			Sensitive: true,
+		}, {
+			Name: "role_arn",
+			Help: `ARN of the IAM role to assume.
+			
+Leave blank if not using assume role.`,
+			Advanced: true,
+		}, {
+			Name: "role_session_name",
+			Help: `Session name for assumed role.
+			
+If empty, a session name will be generated automatically.`,
+			Advanced: true,
+		}, {
+			Name: "role_session_duration",
+			Help: `Session duration for assumed role.
+			
+If empty, the default session duration will be used.`,
+			Advanced: true,
+		}, {
+			Name: "role_external_id",
+			Help: `External ID for assumed role.
+			
+Leave blank if not using an external ID.`,
+			Advanced: true,
 		}, {
 			Name: "upload_concurrency",
 			Help: `Concurrency for multipart uploads and copies.
@@ -927,6 +953,10 @@ type Options struct {
 	SharedCredentialsFile       string               `config:"shared_credentials_file"`
 	Profile                     string               `config:"profile"`
 	SessionToken                string               `config:"session_token"`
+	RoleARN                     string               `config:"role_arn"`
+	RoleSessionName             string               `config:"role_session_name"`
+	RoleSessionDuration         fs.Duration          `config:"role_session_duration"`
+	RoleExternalID              string               `config:"role_external_id"`
 	UploadConcurrency           int                  `config:"upload_concurrency"`
 	ForcePathStyle              bool                 `config:"force_path_style"`
 	V2Auth                      bool                 `config:"v2_auth"`
@@ -1290,6 +1320,34 @@ func s3Connection(ctx context.Context, opt *Options, client *http.Client) (s3Cli
 		opt.Region = "us-east-1"
 	}
 
+	// Handle assume role if RoleARN is specified
+	if opt.RoleARN != "" {
+		fs.Debugf(nil, "Using assume role with ARN: %s", opt.RoleARN)
+
+		// Set region for the config before creating STS client
+		awsConfig.Region = opt.Region
+
+		// Create STS client using the base credentials
+		stsClient := sts.NewFromConfig(awsConfig)
+
+		// Configure AssumeRole options
+		assumeRoleOptions := func(aro *stscreds.AssumeRoleOptions) {
+			// Set session name if provided, otherwise use a default
+			if opt.RoleSessionName != "" {
+				aro.RoleSessionName = opt.RoleSessionName
+			}
+			if opt.RoleSessionDuration != 0 {
+				aro.Duration = time.Duration(opt.RoleSessionDuration)
+			}
+			if opt.RoleExternalID != "" {
+				aro.ExternalID = &opt.RoleExternalID
+			}
+		}
+
+		// Create AssumeRole credentials provider
+		awsConfig.Credentials = stscreds.NewAssumeRoleProvider(stsClient, opt.RoleARN, assumeRoleOptions)
+	}
+
 	provider = loadProvider(opt.Provider)
 	if provider == nil {
 		fs.Logf("s3", "s3 provider %q not known - please set correctly", opt.Provider)

docs/content/s3.md

@@ -745,6 +745,68 @@ If none of these option actually end up providing `rclone` with AWS
 credentials then S3 interaction will be non-authenticated (see the
 [anonymous access](#anonymous-access) section for more info).
 
+#### Assume Role (Cross-Account Access)
+
+If you need to access S3 resources in a different AWS account, you can use IAM role assumption.
+This is useful for cross-account access scenarios where you have credentials in one account
+but need to access resources in another account.
+
+To use assume role, configure the following parameters:
+
+- `role_arn` - The ARN (Amazon Resource Name) of the IAM role to assume in the target account.
+  Format: `arn:aws:iam::ACCOUNT-ID:role/ROLE-NAME`
+- `role_session_name` (optional) - A name for the assumed role session. If not specified,
+  rclone will generate one automatically.
+- `role_session_duration` (optional) - Duration for which the assumed role credentials are valid.
+  If not specified, AWS default duration will be used (typically 1 hour).
+- `role_external_id` (optional) - An external ID required by the role's trust policy for additional security.
+  This is typically used when the role is accessed by a third party.
+
+The assume role feature works with both direct credentials (`env_auth = false`) and environment-based
+authentication (`env_auth = true`). Rclone will first authenticate using the base credentials, then
+use those credentials to assume the specified role.
+
+Example configuration for cross-account access:
+
+```
+[s3-cross-account]
+type = s3
+provider = AWS
+env_auth = true
+region = us-east-1
+role_arn = arn:aws:iam::123456789012:role/CrossAccountS3Role
+role_session_name = rclone-session
+role_external_id = unique-role-external-id-12345
+```
+
+In this example:
+- Base credentials are obtained from the environment (IAM role, credentials file, or environment variables)
+- These credentials are then used to assume the role `CrossAccountS3Role` in account `123456789012`
+- An external ID is provided for additional security as required by the role's trust policy
+
+The target role's trust policy in the destination account must allow the source account or user to assume it.
+Example trust policy:
+
+```json
+{
+  "Version": "2012-10-17",
+  "Statement": [
+    {
+      "Effect": "Allow",
+      "Principal": {
+        "AWS": "arn:aws:iam::SOURCE-ACCOUNT-ID:root"
+      },
+      "Action": "sts:AssumeRole",
+      "Condition": {
+        "StringEquals": {
+          "sts:ExternalID": "unique-role-external-id-12345"
+        }
+      }
+    }
+  ]
+}
+```
+
 ### S3 Permissions
 
 When using the `sync` subcommand of `rclone` the following minimum

go.mod

@@ -25,6 +25,7 @@ require (
 	github.com/aws/aws-sdk-go-v2/credentials v1.18.21
 	github.com/aws/aws-sdk-go-v2/feature/s3/manager v1.20.4
 	github.com/aws/aws-sdk-go-v2/service/s3 v1.90.0
+	github.com/aws/aws-sdk-go-v2/service/sts v1.39.1
 	github.com/aws/smithy-go v1.23.2
 	github.com/buengese/sgzip v0.1.1
 	github.com/cloudinary/cloudinary-go/v2 v2.13.0
@@ -133,7 +134,6 @@ require (
 	github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.19.13 // indirect
 	github.com/aws/aws-sdk-go-v2/service/sso v1.30.1 // indirect
 	github.com/aws/aws-sdk-go-v2/service/ssooidc v1.35.5 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sts v1.39.1 // indirect
 	github.com/bahlo/generic-list-go v0.2.0 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/bodgit/plumbing v1.3.0 // indirect