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In this guide, you will learn how to configure HashiCorp Vault’s AWS Secrets Engine using the assumed_role credential type to obtain temporary, cross-account AWS credentials. Vault runs in Account A (ID ending in 6147) and will assume a role in Account B (ID ending in 2126) to generate scoped credentials.

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Table of Contents

  1. Verify Vault Cluster Health
  2. Prepare Target AWS Account (Account B)
    2.1 Inspect Existing Role (Optional)
    2.2 Create a Customer-Managed Policy
    2.3 Create a Role Trusted by Vault’s Account
  3. Enable & Configure AWS Secrets Engine
  4. Define Vault Role for Cross-Account Access
  5. Generate & Use Temporary Credentials
  6. Flowchart
  7. Conclusion
  8. References

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1. Verify Vault Cluster Health

First, ensure your Vault cluster in Account A is initialized, unsealed, and active. 
vault status
Expected output: 
Key                       Value
Initialized               true
Sealed                    false
Version                   1.6.0+ent
Storage Type              raft
HA Enabled                true

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IAM Role Permissions for Vault EC2 Nodes

Attach a policy to your Vault EC2 instances that permits required AWS API actions:
SidEffectActionResource
PermitEC2ApiAccessForCloudAutoJoinAllowec2:DescribeInstances*
PermitRoute53AccessForLetsEncryptValidationAllowroute53:GetChange, route53:ListHostedZones*
PermitActionsForCloudWatchLogsAllowlogs:CreateLogGroup, logs:CreateLogStream, logs:PutLogEvents, logs:DescribeLogStreamsarn:aws:logs:us-east-1:634211456147:log-group:vault_audit_logs:*
{
  "Statement": [
    {
      "Sid": "PermitEC2ApiAccessForCloudAutoJoin",
      "Effect": "Allow",
      "Action": ["ec2:DescribeInstances"],
      "Resource": "*"
    },
    {
      "Sid": "PermitRoute53AccessForLetsEncryptValidation",
      "Effect": "Allow",
      "Action": ["route53:GetChange", "route53:ListHostedZones"],
      "Resource": "*"
    },
    {
      "Sid": "PermitActionsForCloudWatchLogs",
      "Effect": "Allow",
      "Action": [
        "logs:CreateLogGroup",
        "logs:CreateLogStream",
        "logs:PutLogEvents",
        "logs:DescribeLogStreams"
      ],
      "Resource": "arn:aws:logs:us-east-1:634211456147:log-group:vault_audit_logs:*"
    }
  ]
}

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2. Prepare Target AWS Account (Account B)

In Account B, you will create an IAM policy and role that Vault in Account A can assume.

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2.1 Inspect Existing Role (Optional)

The image shows an AWS Identity and Access Management (IAM) console displaying the summary of a role, including its permissions policies and details like Role ARN, creation time, and maximum session duration.

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2.2 Create a Customer-Managed Policy

Navigate to IAM > Policies > Create policy in the AWS Console and add S3 access permissions: 
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:ListBucketVersions",
        "s3:ListBucket",
        "s3:GetObjectVersion"
      ],
      "Resource": [
        "arn:aws:s3:::bryankrausen/*",
        "arn:aws:s3:::bryankrausen"
      ]
    },
    {
      "Effect": "Allow",
      "Action": ["s3:ListAllMyBuckets", "s3:ListBucket"],
      "Resource": "*"
    }
  ]
}
The image shows the AWS Identity and Access Management (IAM) Management Console with a focus on the "Policies" section, displaying two customer-managed policies related to "vault."

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2.3 Create a Role Trusted by Vault’s Account

  1. Go to IAM > Roles > Create role.
  2. Select Another AWS account as the trusted entity and enter Vault’s Account ID (...6147).
  3. Attach the policy you just created (e.g., vault-role-bucket-access).
  4. Name the role vault-role-bucket-access and complete creation.
The image shows an AWS IAM Management Console screen for creating a role, with options to select the type of trusted entity and choose a use case. In the background, there is a terminal window with some text.
The image shows an AWS IAM Management Console screen where a user is creating a role by selecting a trusted entity type, specifically another AWS account. The background displays a terminal window with some text.

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3. Enable & Configure AWS Secrets Engine

Back in Account A, enable and configure Vault’s AWS Secrets Engine. 
vault secrets enable aws

Success! Enabled the aws secrets engine at: aws/
Next, update the IAM role policy attached to your Vault servers to permit assuming the new cross-account role: 
{
  "Sid": "PermitAccessToCrossAccountRole",
  "Effect": "Allow",
  "Action": "sts:AssumeRole",
  "Resource": [
    "arn:aws:iam::083674922126:role/vault-role-bucket-access"
  ]
}
Apply your changes (for example, via Terraform): 
terraform apply

Apply complete! Resources: 0 added, 1 changed, 0 destroyed.
To support multiple target roles or accounts, add additional role ARNs to the Resource array in the PermitAccessToCrossAccountRole statement.

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4. Define Vault Role for Cross-Account Access

Create a Vault role that references the IAM role in Account B: 
vault write aws/roles/s3_access \
    role_arns=arn:aws:iam::083674922126:role/vault-role-bucket-access \
    credential_type=assumed_role

Success! Data written to: aws/roles/s3_access

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5. Generate & Use Temporary Credentials

  1. Generate STS credentials with a 1-hour TTL: 
    vault write aws/sts/s3_access ttl=1h

    Key                Value
lease_id           aws/sts/s3_access/abcdef123456
lease_duration     1h
access_key         ASIAQBWYRKXZMN3NMZ
secret_key         /gqnjob/P9E/Kg+Wi2nGKAJ6M79iYlMszAUg2
security_token     FQoGZXIvYXdzEJr//////////wEaDM...
  2. Export credentials to your shell: Linux/macOS: 
    export AWS_ACCESS_KEY_ID=ASIAQBWYRKXZMN3NMZ
export AWS_SECRET_ACCESS_KEY=/gqnjob/P9E/Kg+Wi2nGKAJ6M79iYlMszAUg2
export AWS_SESSION_TOKEN=FQoGZXIvYXdzEJr//////////wEaDM...
    Windows PowerShell: 
    SET AWS_ACCESS_KEY_ID=ASIAQBWYRKXZMN3NMZ
SET AWS_SECRET_ACCESS_KEY=/gqnjob/P9E/Kg+Wi2nGKAJ6M79iYlMszAUg2
SET AWS_SESSION_TOKEN=FQoGZXIvYXdzEJr//////////wEaDM...
  3. Use the temporary credentials: 
    aws s3 ls

    2021-08-01 12:00:00 bryankrausen
2021-07-30 09:15:12 krausen-cloudtrail
2021-07-25 17:45:08 vault-advanced

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6. Flowchart

The image is a flowchart illustrating the "Assumed_Role Method" for managing dynamic secrets with AWS, detailing the process of requesting, generating, and revoking AWS credentials using Vault and AWS STS.

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7. Conclusion

You have successfully configured Vault’s AWS Secrets Engine to assume a role in a separate AWS account, generate temporary credentials scoped to that role’s permissions, and consume those credentials to perform cross-account operations. This architecture is highly scalable—simply extend the IAM policy and add Vault roles for additional accounts or use cases.

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8. References

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