How do I prompt for an MFA key to generate and use credentials for AWS CLI access? - bash

Question

I have several Bash scripts that invoke AWS CLI commands for which permissions have changed to require MFA, and I want to be able to prompt for a code generated by my MFA device in these scripts so that they can run with the necessary authentication.
But there seems to be no simple built in way to do this. The only documentation I can find involves a complicated process of using aws sts get-session-token and then saving each value in a configuration, which it is then unclear how to use.
To be clear what I'd like is that when I run one of my scripts that that contains AWS CLI commands that require MFA, I'm simply prompted for the code, so that providing it allows the AWS CLI operations to complete. Something like:
#!/usr/bin/env bash
# (1) prompt for generated MFA code
# ???
# (2) use entered code to generate necessary credentials
aws sts get-session-token ... --token-code $ENTERED_VALUE
# (3) perform my AWS CLI commands requiring MFA
# ....
It's not clear to me how to prompt for this when needed (which is probably down to not being proficient with bash) or how to use the output of get-session-token once I have it.
Is there a way to do what I'm looking for?
I've tried to trigger a prompt by specifying a --profile with a mfa_serial entry; but that doesn't work either.

Answer 1

Ok after spending more time on this script with a colleague - we have come up with a much simpler script. This does all the credential file work for you , and is much easier to read. It also allows for all your environments new tokens to be in the same creds file. The initial call to get you MFA requires your default account keys in the credentials file - then it generates your MFA token and puts them back in the credentials file.
#!/usr/bin/env bash
function usage {
echo "Example: ${0} dev 123456 "
exit 2
}
if [ $# -lt 2 ]
then
usage
fi
MFA_SERIAL_NUMBER=$(aws iam list-mfa-devices --profile bh${1} --query 'MFADevices[].SerialNumber' --output text)
function set-keys {
aws configure set aws_access_key_id ${2} --profile=${1}
aws configure set aws_secret_access_key ${3} --profile=${1}
aws configure set aws_session_token ${4} --profile=${1}
}
case ${1} in
dev|qa|prod) set-keys ${1} $(aws sts get-session-token --profile bh${1} --serial-number ${MFA_SERIAL_NUMBER} --query 'Credentials.[AccessKeyId,SecretAccessKey,SessionToken]' --output text --token-code ${2});;
*) usage ;;
esac

Answer 2

Inspired by #strongjz and #Nick answers, I wrote a small Python command to which you can pipe the output of the aws sts command.
To install:
pip install sts2credentials
To use:
aws sts get-session-token \
--serial-number arn:aws:iam::123456789012:mfa/your-iam-user \
--token-code 123456 \
--profile=your-profile-name \
| sts2credentials
This will automatically add the access key ID, the secret access key, and the session token under a new "sts" profile in your ~/.aws/credentials file.

Answer 3

For bash you could read in the value, then set those values from the sts output
echo "Type the mfa code that you want to use (4 digits), followed by [ENTER]:"
read ENTERED_VALUE
aws sts get-session-token ... --token-code $ENTERED_VALUE
then you'll have to parse the output of the sts call which has the access key, secret and session token.
{
Credentials: {
AccessKeyId: "ASIAJPC6D7SKHGHY47IA",
Expiration: 2016-06-05 22:12:07 +0000 UTC,
SecretAccessKey: "qID1YUDHaMPet5xw/vpw1Wk8SKPilFihdiMSdSIj",
SessionToken: "FQoDYXdzEB4aDLwmzouEQ3eckfqJxyLOARbBGasdCaAXkZ7ABOcOCNx2/7sS8N7A6Dpcax/t2G8KNTcUkRLdxI0gTvPoKQeZrH8wUrL4UxFFP6kCWEasdVIBAoUfuhdeUa1a7H216Mrfbbv3rMGsVKUoJT2Ar3r0pYgsYxizOWzH5VaA4rmd5gaQvfSFmasdots3WYrZZRjN5nofXJBOdcRd6J94k8m5hY6ClfGzUJEqKcMZTrYkCyUu3xza2S73CuykGM2sePVNH9mGZCWpTBcjO8MrawXjXj19UHvdJ6dzdl1FRuKdKKeS18kF"
}
}
then set them
aws configure set aws_access_key_id default_access_key --profile NAME_PROFILE
aws configure set aws_secret_access_key default_secret_key --profile NAME_PROFILE
aws configure set default.region us-west-2 --profile
aws some_commmand --profile NAME_PROFILE
http://www.tldp.org/LDP/Bash-Beginners-Guide/html/sect_08_02.html
AWS STS API Reference
http://docs.aws.amazon.com/STS/latest/APIReference/API_GetSessionToken.html
AWS CLI STS Command
http://docs.aws.amazon.com/cli/latest/reference/sts/get-session-token.html
I wrote something very similar to what you are trying to in Go, here but this is for the sts assumerole not get-session-token.

Answer 4

I wrote a simple script to set the AWS credentials file for a profile called mfa. Then all bash scripts you write just need to have the "--profile mfa" added so they will just work. This also allows for multiple AWS accounts - as many of us have those these days. I'm sure this can be improved - but it was quick and dirty and does what you want and everything I need.
You will have to amend facts in the script to fit your account details - I have marked them clearly with chevrons < >. NB Obviously once you have populated the script with all your details it is not to be copied about - unless you want unintended consequences. This uses recursion within the credentials file - as the standard access keys are called each time to create the mfa security tokens.
#!/bin/bash
# Change for your username - would be /home/username on Linux/BSD
dir='/Users/<your-user-name>'
region=us-east-1
function usage {
echo "Must enter mfa token and then either dev/qa/prod"
echo "i.e. mfa-set-aws-profile.sh 123456 qa"
exit 2
}
if [[ $1 == "" ]]
then
echo "Must give me a token - how do you expect this to work - DOH :-)"
usage
exit 2
fi
# Write the output from sts command to a json file for parsing
# Just add accounts below as required
case $2 in
dev) aws sts get-session-token --profile dev --serial-number arn:aws:iam::<123456789>:mfa/<john.doe> --token-code $1 > $dir/mfa-json;;
qa) aws sts get-session-token --profile qa --serial-number arn:aws:iam::<123456789>:mfa/<john.doe> --token-code $1 > $dir/mfa-json;;
-h) usage ;;
*) usage ;;
esac
# Remove quotes and comma's to make the file easier to parse -
# N.B. gsed is for OSX - on Linux/BSD etc sed should be just fine.
/usr/local/bin/gsed -i 's/\"//g;s/\,//g' $dir/mfa-json
# Parse the mfa info into vars for use in aws credentials file
seckey=`cat $dir/mfa-json | grep SecretAccessKey | gsed -E 's/[[:space:]]+SecretAccessKey\: //g'`
acckey=`cat $dir/mfa-json | grep AccessKeyId | gsed 's/[[:space:]]+AccessKeyId\: //g'`
sesstok=`cat $dir/mfa-json | grep SessionToken | gsed 's/[[:space:]]+SessionToken\: //g'`
# output all the gathered info into your aws credentials file.
cat << EOF > $dir/.aws/credentials
[default]
aws_access_key_id = <your normal keys here if required>
aws_secret_access_key = <your normal keys here if required>
[dev]
aws_access_key_id = <your normal keys here >
aws_secret_access_key = <your normal keys here >
[qa]
aws_access_key_id = <your normal keys here >
aws_secret_access_key = <your normal keys here >
[mfa]
output = json
region = $region
aws_access_key_id = $acckey
aws_secret_access_key = $seckey
aws_session_token = $sesstok
EOF