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Even - SSH Access Granting Service

SSH access granting service to distribute personal public SSH keys on demand.

Idea

Users can request temporary SSH access to servers by calling the "SSH Access Granting Service" which puts their public SSH key in place.

  • The user needs to authenticate against the service (via OAuth2 access token)
  • The user requests temporary SSH access for a certain host (POST /access-requests)
  • The service checks whether the user is allowed to gain access to the specified host by checking if the hostname follows the given pattern (HTTP_ALLOWED_HOSTNAME_TEMPLATE)
  • The service instructs the host to grant access via a SSH forced command script
  • The forced command script downloads the user's public SSH key from the service (the public SSH key is read from the HTTP endpoint given by USERSVC_SSH_PUBLIC_KEY_URL_TEMPLATE)
  • The forced command script configures the /home/<user>/.ssh/authorized_keys file accordingly

Grant SSH access flow

Development

The service is written in Clojure. You need Leiningen installed to build or develop.

To start a web server for the application, run:

$ export CREDENTIALS_DIR=. # to make "tokens" library happy
$ export OAUTH2_ACCESS_TOKENS=user-service=abc123-456 # fixed token for local development
$ export .. # see configuration section below
$ lein repl
=> (go)

The service is now exposing its HTTP REST API under http://localhost:8080/.

Requesting access to server "127.0.0.1" for user "jdoe":

$ curl -XPOST -H Content-Type:application/json -H 'Authorization: Bearer mytoken' --data '{"hostname": "127.0.0.1", "reason": "test"}' http://localhost:8080/access-requests

Building

To build a deployable artifact, use the uberjar task, that produces a single JAR file, that every JVM should be able to execute.

$ lein do uberjar, scm-source, docker build

Running

Running the previously built Docker image and passing configuration via environment variables:

$ docker run -p 8080:8080 -e AWS_REGION_ID=eu-west-1 -e CREDENTIALS_DIR=/ -e HTTP_TEAM_SERVICE_URL=https://teams.example.org -e HTTP_TOKENINFO_URL=https://oauth2.example.org/tokeninfo -e HTTP_ALLOWED_HOSTNAME_TEMPLATE="odd-[a-z0-9-]*.{team}.example.org" -e OAUTH2_ACCESS_TOKEN_URL=https://oauth2.example.org/access_token -e USERSVC_SSH_PUBLIC_KEY_URL_TEMPLATE=https://users.example.org/{user}/ssh -e SSH_PRIVATE_KEY="$SSH_PRIVATE_KEY" stups/even

All configuration values can be passed encrypted when running on AWS (this is supported by the underlying Friboo library):

$ aws kms encrypt --key-id 123 --plaintext "secret" # encrypt with KMS
$ export SSH_PRIVATE_KEY="aws:kms:<KMS-CIPHERTEXT-BLOB>"

Configuration

The following configuration parameters can/should be passed via environment variables:

AWS_REGION_ID
Optional AWS region ID to use for KMS decryption (e.g. "eu-west-1").
CREDENTIALS_DIR
Folder with OAuth2 application credentials (user.json and client.json) --- this is automatically set when running on the Taupage AMI.
HTTP_TEAM_SERVICE_URL
URL of the Team Service to check team membership for authorization.
HTTP_TOKENINFO_URL
URL to OAuth2 token info endpoint.
HTTP_ALLOWED_HOSTNAME_TEMPLATE
Regex template for the allowed hostname. "{team}" will be replaced by the user's team ID. Example: "odd-[a-z0-9-]*.{team}.example.org"
OAUTH2_ACCESS_TOKEN_URL
URL to OAuth2 provider endpoint to get a new service access token.
SSH_AGENT_FORWARDING
Boolean flag whether to use agent forwarding (-A). Agent forwarding is necessary for bastion host support.
SSH_PORT
SSH port number to use (default: 22).
SSH_PRIVATE_KEYS
The SSH private keys in PEM format. Can be encrypted, since KMS doesn't support data larger than 4k.
SSH_PRIVATE_KEY_PASSWORD
Password for the SSH keys, optional.
SSH_USER
The SSH username on remote servers (default: "granting-service").
USERSVC_CACHE_BUCKET
Optional S3 bucket name to use for caching SSH public keys (to bridge potential downtimes of upstream HTTP service).
USERSVC_SSH_PUBLIC_KEY_URL_TEMPLATE
URL template for the public SSH key endpoints ("{user}" will be replaced with the user's ID/username). Example: "https://users.example.org/employees/{user}/ssh"

Requesting SSH Access

Users can use the convenience script Piu instead of doing a manual HTTP POST.

$ sudo pip3 install --upgrade stups-piu
$ piu 172.31.0.1 "testing the piu script"

License

Copyright © 2015 Zalando SE

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.