How to securely manage credentials to multiple AWS accounts

Table Of Contents

Problem space

As soon as you start working with more than one project or organization at AWS cloud, the first question you may have is how to manage awscli credentials and have to use them easily and securely to get access to all your AWS accounts and environments.

I always was not a big fan of ~/.aws/credentials file, because every single time I was coming to a new customer, I needed to open this file for the edit to add new credentials. As a result, I constantly had a feeling, that I displayed all my existing credentials to all security cameras in the office. God, bless the inventor of the privacy screens!

The second problem with credentials is that they need to be renewed from time to time. The more accounts you have, the more efforts you spend on credentials rotation.

And the third problem - is assuming roles in terminal sessions and working in several different environments at the same time.

Solution

As a solution for the first two problems, not too far ago I started using:

aws-vault - AWS credentials manager

As a solution for the last two problems, I found that the following tooling stack suits most of my needs:

zsh and oh-my-zsh - terminal
zsh-aws-vault - AWS environment highlighting for the terminal session

Managing AWS credentials

Here’s a quick getting started guide.

Installation

I’m assuming here, that you already have zsh and oh-my-zsh installed. 😎

Let’s install aws-vault. Here’s the complete list of installation steps for most available platforms.

We’ll be doing everything for OS X:

brew cask install aws-vault

Choosing aws-vault backend

aws-vault supports several backends to store your credentials. My preference is to use an encrypted file. So, you need to add the following variable to your ~/.zshrc:

export AWS_VAULT_BACKEND="file"

Moving credentials

Now open your ~/.aws/credentials file. For every existing profile add credentials to aws-vault

cat ~/.aws/credentials

aws-vault add <profile_1>
aws-vault add <profile_2>

Now, aws-vault has AWS_VAULT_FILE_PASSPHRASE variable, which can be used to stop aws-vault from asking your vault password over and over again. There’re two ways to use it:

Not secure

Add the following variable to your ~/.zshrc or ~/.bashrc file, to prevent aws-vault for asking for your password every single time:

export AWS_VAULT_FILE_PASSPHRASE="my_strong_password"

Secure

Instead of storing AWS_VAULT_FILE_PASSPHRASE variable in .*rc files, you may create AWS Systems Manager Parameter Store SecureString parameter, which contains your aws-vault password:

aws ssm put-parameter \
  --name '/laptop/aws-vault/password' \
  --description 'aws-vault password on my laptop' \
  --value 'my_super_secret_password' \
  --type SecureString

Let’s create wrapper script, which will call aws-vault call aws-vault and set up AWS_VAULT_FILE_PASSPHRASE with necessary value from AWS Systems Manager Parameter Store:

mkdir -p $HOME/bin
cat > $HOME/bin/call-aws-vault.sh <<- EOF
#!/usr/bin/env bash

export PROFILE=\$1
export AWS_VAULT_FILE_PASSPHRASE=\$(aws ssm get-parameters --profile default --names '/laptop/aws-vault/password' --with-decryption --query 'Parameters[0].Value' --output text)

aws-vault exec -j \$PROFILE
EOF

chmod +x $HOME/bin/call-aws-vault.sh

Now you may use this wrapper at ~/.aws/config like that:

[profile my_new_profile]
credential_process = /<full_path_to_your_home_folder>/bin/call-aws-vault.sh my_new_profile

You may rename ~/.aws/credentials and later on completely delete it as soon as you test everything.

Switching AWS profiles

To list all your AWS profiles, just type:

aws-vault list

Great, now you can easily switch your environment and see, where you’re working:

aws-vault exec <profile_name>

Here’s how it finally looks like:

Role-based approach

Well, ok, we just moved all our AWS credentials to a secure vault and configured our terminal to display our current aws-vault session. Now it’s time to discuss, how we can improve the solution even more.

Multi-account organization

One of best practices for organizing AWS users' access to different AWS accounts - is managing all IAM users in one AWS account and providing access to another AWS accounts by allowing them to consume roles (sts:AssumeRole call) from that accounts.

Here’s the typical AWS Organization example:

AWS provided a great explanation of How to Use a Single IAM User to Easily Access All Your Accounts by Using the AWS CLI in their blog post, where they describing role consuming process and awscli configuration. I’ll not copy-paste them. Instead, we’ll concentrate on aws-vault configuration to do a similar thing, but without ~/.aws/credentials file.

Assuming you already have all the necessary grants and permissions between your accounts… If not, here’s the great article on that topic - Tutorial: Delegate Access Across AWS Accounts Using IAM Roles.

Default profile setup

You should already have your default profile setup in place at ~/.aws/config file. Probably, it looks something like that:

[profile default]
region = us-east-1

Let’s configure aws-vault as a credential source for our default profile:

[profile default]
region = us-east-1
credential_process = /usr/local/bin/aws-vault exec -j default

Now, if you grant permissions to your user or role from default profile to assume AWS role from another account, you’ll be able to specify new profiles configuration like that:

[profile default]
region = us-east-1
credential_process = /usr/local/bin/aws-vault exec -j default
mfa_serial = arn:aws:iam::<account_id>:mfa/admin

[profile account_1_role_admin]
region = us-east-1
role_arn = arn:aws:iam::<account_id>:role/admin
source_profile = default

[profile account_2_role_qa]
region = us-east-1
role_arn = arn:aws:iam::<account_id>:role/qa
source_profile = default

source_profile configuration option will tell awscli, which account to use to grab role for any given profile.

Testing

The fastest way to test, that you’re able to assume the role, is to call:

aws sts get-caller-identify

You should see something similar for your default profile:

{
    "UserId": "AIDDRCTFVGBHNJMGF3WI7R",
    "Account": "01234567890",
    "Arn": "arn:aws:iam::01234567890:user/admin"
}

To test any other profile call:

aws sts get-caller-identity --profile account_1_role_admin

You should see output similar to the following:

{
    "UserId": "AROALKJHGFGDFV3IR2VSI:botocore-session-1584897134",
    "Account": "012345678901",
    "Arn": "arn:aws:sts::012345678901:assumed-role/admin/botocore-session-1584897134"
}

As a small bonus to those of you, who came to the end, here’s how to login to AWS web console for every given profile:

aws-vault login <profile name>

Summary

Using zsh, aws-vault, and AWS sts:AssumeRole feature together can significantly simplify and make more secure management of multiple AWS accounts and their credentials.

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Authors

Andrei Maksimov

I’m a passionate Cloud Infrastructure Architect with more than 15 years of experience in IT.

Let’s discuss your AWS questions if you still have them.

This post represents my personal experience and opinion about the topic.