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Credentials-fetcher is a Linux daemon that retrieves gMSA credentials from Active Directory over LDAP. It creates and refreshes kerberos tickets from gMSA credentials. Kerberos tickets can be used by containers to run apps/services that authenticate using Active Directory.

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aws/credentials-fetcher

Credentials Fetcher

credentials-fetcher is a Linux daemon that retrieves gMSA credentials from Active Directory over LDAP. It creates and refreshes kerberos tickets from gMSA credentials. Kerberos tickets can be used by containers to run apps/services that authenticate using Active Directory.

This daemon works in a similar way as ccg.exe and the gMSA plugin in Windows as described in - https://docs.microsoft.com/en-us/virtualization/windowscontainers/manage-containers/manage-serviceaccounts#gmsa-architecture-and-improvements

How to install and run

On Fedora 36 and similar distributions, the binary RPM can be installed as sudo dnf install credentials-fetcher. You can also use yum if dnf is not present. The daemon can be started using sudo systemctl start credentials-fetcher.

On Enterprise Linux 9 ( RHEL | CentOS | AlmaLinux ), the binary can be installed from EPEL. To add EPEL, see the EPEL Quickstart. Once EPEL is enabled, install credentials-fetcher with sudo dnf install credentials-fetcher.

For other linux distributions, the daemon binary needs to be built from source code.

Development

Prerequisites

Create credentialspec associated with gMSA account:

  • Create a domain joined windows instance
  • Install powershell module - "Install-Module CredentialSpec"
  • New-CredentialSpec -AccountName WebApp01 // Replace 'WebApp01' with your own gMSA
  • You will find the credentialspec in the directory 'C:\Program Data\Docker\Credentialspecs\WebApp01_CredSpec.json'

Standalone mode

To start a local dev environment from scratch:

* Clone the Git repository.
* cd credentials-fetcher && mkdir build
* cd build && cmake ../ && make -j
* ./credentials-fetcher to start the program in non-daemon mode.

Testing

To communicate with the daemon over gRPC, install grpc-cli. For example sudo yum install grpc-cli

AddKerberosLease API:

Note: APIs use unix domain socket

Invoke the AddkerberosLease API with the credentialsspec input as shown:
grpc_cli call {unix_domain_socket} AddKerberosLease "credspec_contents: '{credentialspec}'"

Sample:
grpc_cli call unix:/var/credentials-fetcher/socket/credentials_fetcher.sock
AddKerberosLease "credspec_contents: '{\"CmsPlugins\":[\"ActiveDirectory\"],\"DomainJoinConfig\":{\"Sid\":\"S-1-5-21-4217655605-3681839426-3493040985\",
\"MachineAccountName\":\"WebApp01\",\"Guid\":\"af602f85-d754-4eea-9fa8-fd76810485f1\",\"DnsTreeName\":\"contoso.com\",
\"DnsName\":\"contoso.com\",\"NetBiosName\":\"contoso\"},\"ActiveDirectoryConfig\":{\"GroupManagedServiceAccounts\":[{\"Name\":\"WebApp01\",\"Scope\":\"contoso.com\"}
,{\"Name\":\"WebApp01\",\"Scope\":\"contoso\"}]}}'"

* Response:
  lease_id - unique identifier associated to the request
  created_kerberos_file_paths - Paths associated to the Kerberos tickets created corresponding to the gMSA accounts
DeleteKerberosLease API:
Invoke the Delete kerberosLease API with lease id input as shown:
grpc_cli call {unix_domain_socket} DeleteKerberosLease "lease_id: '{lease_id}'"

Sample:
grpc_cli call unix:/var/credentials-fetcher/socket/credentials_fetcher.sock DeleteKerberosLease "lease_id: '${response_lease_id_from_add_kerberos_lease}'"

* Response:
    lease_id - unique identifier associated to the request
    deleted_kerberos_file_paths - Paths associated to the Kerberos tickets deleted corresponding to the gMSA accounts

Logging

Logs about request/response to the daemon and any failures.

journalctl -u credentials-fetcher

Default environment variables

Environment Key Examples values Description
CF_KRB_DIR '/var/credentials-fetcher/krbdir' (Default) Dir path for storing the kerberos tickets
CF_UNIX_DOMAIN_SOCKET_DIR '/var/credentials-fetcher/socket' (Default) Dir path for the domain socker for gRPC communication 'credentials_fetcher.sock'
CF_LOGGING_DIR '/var/credentials-fetcher/logging' (Default) Dir Path for log
CF_TEST_DOMAIN_NAME 'contoso.com' Test domain name
CF_TEST_GMSA_ACCOUNT 'webapp01' Test gMSA account name

Runtime environment variables

Environment Variable Examples values Description
CF_CRED_SPEC_FILE '/var/credentials-fetcher/my-credspec.json' Path to a credential spec file used as input. (Lease id default: credspec)
'/var/credentials-fetcher/my-credspec.json:myLeaseId' An optional lease id specified after a colon
CF_GMSA_OU 'CN=Managed Service Accounts' Component of GMSA distinguished name (see docs/cf_gmsa_ou.md)

Examples

Testing with Active Directory domain-joined mode (opensource)

Credentials-fetcher in domainless mode assuming gMSA account 'WebApp01' has been setup as per https://learn.microsoft.com/en-us/virtualization/windowscontainers/manage-containers/manage-serviceaccounts#use-case-for-creating-gmsa-account-for-domain-joined-container-hosts

  • Either launch Amazon-Linux 2023 instance or build from source and run.

  • Make sure the instance/server is domain-joined using the realm list command in Linux.

  • Make sure Credentials-fetcher is running using:

     journalctl -u credentials-fetcher
    
  • Install grpc for python as per https://grpc.io/docs/languages/python/quickstart/

  • Create the grpc pb2 files using credentialsfetcher.proto:

    # python3 -m grpc_tools.protoc -I. --python_out=. --grpc_python_out=. credentialsfetcher.proto
    
  • Copy this code (Create the credspec and add it to the script as below ) (Alternatively, configure using the managed services at AWS ECS mode and AWS Fargate mode )

       # cat credentials_fetcher_client.py
       import grpc
       import credentialsfetcher_pb2
       import credentialsfetcher_pb2_grpc
    
       def run():
       with grpc.insecure_channel('unix:///var/credentials-fetcher/socket/credentials_fetcher.sock') as channel:
           stub = credentialsfetcher_pb2_grpc.CredentialsFetcherServiceStub(channel)
           credspec_contents="{\"CmsPlugins\":[\"ActiveDirectory\"],\"DomainJoinConfig\":{\"Sid\":\"S-1-5-21-2725122404-4129967127-2630707939\",\"MachineAccountName\":\"WebApp01\",\"Guid\":\"e96e0e09-9305-462f-9e44-8a8179722897\",\"DnsTreeName\":\"contoso.com\",\"DnsName\":\"contoso.com\",\"NetBiosName\":\"contoso\"},\"ActiveDirectoryConfig\":{\"GroupManagedServiceAccounts\":[{\"Name\":\"WebApp01\",\"Scope\":\"contoso.com\"},{\"Name\":\"WebApp01\",\"Scope\":\"contoso\"}]}}"
           contents = []
           contents += [credspec_contents]
           response = stub.AddKerberosLease(credentialsfetcher_pb2.CreateKerberosLeaseRequest(credspec_contents = contents))
           print(f"Server response: {response}")
    
       if __name__ == '__main__':
           run()
    
  • Configure Credentials-fetcher to create tickets for the 'WebApp01' gMSA account.

    # python3 credentials_fetcher_client.py
        Server response: lease_id: "94efba947d75728bbf70"
        created_kerberos_file_paths: "/var/credentials-fetcher/krbdir/94efba947d75728bbf70/WebApp01"
    
  • Here is the resulting kerberos ticket that can be shared

      # klist  /var/credentials-fetcher/krbdir/94efba947d75728bbf70/WebApp01/krb5cc
          Ticket cache: FILE:/var/credentials-fetcher/krbdir/94efba947d75728bbf70/WebApp01/krb5cc
          Default principal: WebApp01$@CONTOSO.COM
    
    Valid starting     Expires            Service principal
    07/17/24 22:42:42  07/18/24 08:42:42  krbtgt/CONTOSO.COM@CONTOSO.COM
      renew until 07/24/24 22:42:42
    

Testing with Active Directory domainless mode (opensource )

Credentials-fetcher in domainless mode assuming gMSA account 'WebApp01' has been setup as per https://learn.microsoft.com/en-us/virtualization/windowscontainers/manage-containers/manage-serviceaccounts#use-case-for-creating-gmsa-account-for-non-domain-joined-container-hosts ( Please substitute username, secret and password as needed)

#  cat credentials_fetcher_client.py

    import grpc
    import credentialsfetcher_pb2
    import credentialsfetcher_pb2_grpc

    def run():
        with grpc.insecure_channel('unix:///var/credentials-fetcher/socket/credentials_fetcher.sock') as channel:
            stub = credentialsfetcher_pb2_grpc.CredentialsFetcherServiceStub(channel)
            credspec_contents="{\"CmsPlugins\":[\"ActiveDirectory\"],\"DomainJoinConfig\":{\"Sid\":\"S-1-5-21-2725122404-4129967127-2630707939\",\"MachineAccountName\":\"WebApp01\",\"Guid\":\"e96e0e09-9305-462f-9e44-8a8179722897\",\"DnsTreeName\":\"contoso.com\",\"DnsName\":\"contoso.com\",\"NetBiosName\":\"contoso\"},\"ActiveDirectoryConfig\":{\"GroupManagedServiceAccounts\":[{\"Name\":\"WebApp01\",\"Scope\":\"contoso.com\"},{\"Name\":\"WebApp01\",\"Scope\":\"contoso\"}]}}"
            contents = []
            contents += [credspec_contents]
            response = stub.AddNonDomainJoinedKerberosLease(credentialsfetcher_pb2.CreateNonDomainJoinedKerberosLeaseRequest(credspec_contents = contents, username="admin", password="mypassword", domain="contoso.com"))
            print(f"Server response: {response}")

    if __name__ == '__main__':
        run()
  • Configure Credentials-fetcher (in opensource mode) to create tickets for the 'WebApp01' gMSA account ( Alternatively, configure using the managed services at AWS ECS mode and AWS Fargate mode)

    # python3 credentials_fetcher_client.py
    
        Server response: lease_id: "34e2b89e3fd8a9bcb297"
        created_kerberos_file_paths: "/var/credentials-fetcher/krbdir/34e2b89e3fd8a9bcb297/WebApp01"
    
  • Here is the resulting kerberos ticket that can be shared

    # klist  /var/credentials-fetcher/krbdir/34e2b89e3fd8a9bcb297/WebApp01/krb5cc
    
        Ticket cache: FILE:/var/credentials-fetcher/krbdir/34e2b89e3fd8a9bcb297/WebApp01/krb5cc
        Default principal: WebApp01$@CONTOSO.COM
    
        Valid starting     Expires            Service principal
        07/17/24 22:10:29  07/18/24 08:10:29  krbtgt/CONTOSO.COM@CONTOSO.COM
            renew until 07/18/24 22:10:29
    

Compatibility

Running the Credentials-fetcher outside of Linux distributions is not supported.

Contributing

Contributions and feedback are welcome! Proposals and pull requests will be considered and responded to. For more information, see the CONTRIBUTING.md file. If you have a bug/and issue around the behavior of the credentials-fetcher, please open it here.

Amazon Web Services does not currently provide support for modified copies of this software.

Security disclosures

If you think you’ve found a potential security issue, please do not post it in the Issues. Instead, please follow the instructions here or email AWS security directly.

License

The Credentials Fetcher is licensed under the Apache 2.0 License. See LICENSE and NOTICE for more information.

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Credentials-fetcher is a Linux daemon that retrieves gMSA credentials from Active Directory over LDAP. It creates and refreshes kerberos tickets from gMSA credentials. Kerberos tickets can be used by containers to run apps/services that authenticate using Active Directory.

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