diff --git a/src/sshecret/backend/__init__.py b/src/sshecret/backend/__init__.py
new file mode 100644
index 0000000..be1b7d5
--- /dev/null
+++ b/src/sshecret/backend/__init__.py
@@ -0,0 +1,28 @@
+"""SSHecret backend."""
+
+from .api import SshecretBackend
+from .models import (
+    AuditLog,
+    Client,
+    ClientFilter,
+    ClientReference,
+    ClientSecret,
+    DetailedSecrets,
+    Policy,
+    Secret,
+    FilterType,
+)
+
+
+__all__ = [
+    "AuditLog",
+    "Client",
+    "ClientFilter",
+    "ClientReference",
+    "ClientSecret",
+    "DetailedSecrets",
+    "FilterType",
+    "Policy",
+    "Secret",
+    "SshecretBackend",
+]
diff --git a/src/sshecret/backend/api.py b/src/sshecret/backend/api.py
new file mode 100644
index 0000000..c35db51
--- /dev/null
+++ b/src/sshecret/backend/api.py
@@ -0,0 +1,350 @@
+"""Backend client.
+
+"""
+
+import logging
+from typing import Any, Self
+import httpx
+
+from pydantic import TypeAdapter
+
+from .models import (
+    AuditLog,
+    Client,
+    ClientSecret,
+    ClientQueryResult,
+    ClientFilter,
+    DetailedSecrets,
+    Secret,
+)
+from .exceptions import BackendValidationError, BackendConnectionError
+from .utils import validate_public_key
+
+LOG = logging.getLogger(__name__)
+
+
+class ClientQueryIterator:
+    """Asynchronous query iterator."""
+
+    def __init__(
+        self,
+        client: httpx.AsyncClient,
+        filter_params: ClientFilter | None = None,
+    ) -> None:
+        """Create a query iterator."""
+        self.client: httpx.AsyncClient = client
+        if not filter_params:
+            filter_params = ClientFilter()
+        self.filter_params: ClientFilter = filter_params
+
+        self._result: ClientQueryResult | None = None
+        self._clients: list[Client] = []
+        self.offset: int = 0
+
+    async def _get_batch(self) -> None:
+        """Get batch."""
+        params: dict[str, str | int] = {
+            **self.filter_params.get_params(),
+            "offset": self.offset,
+        }
+        try:
+            results = await self.client.get("/api/v1/clients/", params=params)
+        except httpx.TransportError as e:
+            raise BackendConnectionError() from e
+        if results.status_code != 200:
+            raise BackendConnectionError()
+        self._result = ClientQueryResult.model_validate(results.json())
+        self._clients = self._result.clients
+
+    async def get_next_client(self) -> Client | None:
+        """Get next client.
+
+        When do we know when to stop?
+        """
+        if not self._result:
+            await self._get_batch()
+        assert self._result is not None
+        if self._result.total_results == self.offset:
+            return None
+        if not self._clients:
+            await self._get_batch()
+
+        client = self._clients.pop(0)
+        self.offset += 1
+        return client
+
+    def __aiter__(self) -> Self:
+        """Iterate async."""
+        return self
+
+    async def __anext__(self) -> Client:
+        """Get next client."""
+        if client := await self.get_next_client():
+            return client
+        raise StopAsyncIteration
+
+
+class SshecretBackend:
+    """Backend interface."""
+
+    def __init__(self, backend_url: str, api_token: str) -> None:
+        """Initialize backend client."""
+
+        url = httpx.URL(backend_url)
+
+        self.http_client: httpx.AsyncClient = httpx.AsyncClient(
+            headers={"X-Api-Token": api_token},
+            base_url=url,
+        )
+        self.sync_client: httpx.Client = httpx.Client(
+            headers={"X-Api-Token": api_token},
+            base_url=url,
+        )
+
+    async def _get(self, path: str) -> httpx.Response:
+        """Perform a get request."""
+        try:
+            return await self.http_client.get(path)
+        except httpx.ConnectError as e:
+            raise BackendConnectionError() from e
+
+    async def _delete(self, path: str) -> httpx.Response:
+        """Perform a delete request."""
+        try:
+            return await self.http_client.delete(path)
+        except httpx.ConnectError as e:
+            raise BackendConnectionError() from e
+
+    async def _post(self, path: str, json: Any | None = None) -> httpx.Response:
+        """Perform a POST request."""
+        try:
+            return await self.http_client.post(path, json=json)
+        except httpx.ConnectError as e:
+            raise BackendConnectionError() from e
+
+    async def _put(self, path: str, json: Any | None = None) -> httpx.Response:
+        """Perform a PUT request."""
+        try:
+            return await self.http_client.put(path, json=json)
+        except httpx.ConnectError as e:
+            raise BackendConnectionError() from e
+
+    async def request(self, path: str) -> httpx.Response:
+        """Send a simple GET request."""
+        response = await self._get(path)
+        return response
+
+    async def create_client(
+        self, name: str, public_key: str, description: str | None = None
+    ) -> None:
+        """Register a new client."""
+        if not validate_public_key(public_key):
+            raise BackendValidationError("Error: Invalid public key format.")
+        data = {
+            "name": name,
+            "public_key": public_key,
+        }
+        if description:
+            data["description"] = description
+        path = "/api/v1/clients/"
+        response = await self._post(path, json=data)
+
+        response.raise_for_status()
+
+    async def get_clients(self, filter: ClientFilter | None = None) -> list[Client]:
+        """Get all clients."""
+        clients: list[Client] = []
+        async for client in ClientQueryIterator(self.http_client, filter):
+            clients.append(client)
+
+        return clients
+
+    async def get_client(self, name: str) -> Client | None:
+        """Lookup a client on username."""
+        path = f"/api/v1/clients/{name}"
+        response = await self.request(path)
+        if response.status_code == 404:
+            return None
+        response.raise_for_status()
+        client = Client.model_validate(response.json())
+        return client
+
+    async def get_client_by_id(self, id: str) -> Client | None:
+        """Lookup a client on username."""
+        path = f"/api/v1/clients/id/{id}"
+        response = await self.request(path)
+        if response.status_code == 404:
+            return None
+        response.raise_for_status()
+        client = Client.model_validate(response.json())
+        return client
+
+    async def delete_client(self, client_name: str) -> None:
+        """Delete a client."""
+        path = f"/api/v1/clients/{client_name}"
+        response = await self._delete(path)
+
+        response.raise_for_status()
+
+    async def delete_client_by_id(self, id: str) -> None:
+        """Delete a client."""
+        path = f"/api/v1/clients/id/{id}"
+        response = await self._delete(path)
+
+        response.raise_for_status()
+
+    async def create_client_secret(
+        self, client_name: str, secret_name: str, encrypted_secret: str
+    ) -> None:
+        """Create a secret.
+
+        This will overwrite any existing secret with that name.
+        """
+        path = f"api/v1/clients/{client_name}/secrets/{secret_name}"
+        response = await self._put(path, json={"value": encrypted_secret})
+
+        response.raise_for_status()
+
+    async def get_client_secret(self, name: str, secret_name: str) -> str:
+        """Fetch a secret."""
+        path = f"/api/v1/clients/{name}/secrets/{secret_name}"
+        response = await self.request(path)
+        response.raise_for_status()
+        secret = ClientSecret.model_validate(response.json())
+        return secret.secret
+
+    async def delete_client_secret(self, client_name: str, secret_name: str) -> None:
+        """Delete a secret from a client."""
+        path = f"api/v1/clients/{client_name}/secrets/{secret_name}"
+        response = await self._delete(path)
+
+        response.raise_for_status()
+
+    async def update_client(self, client: Client) -> Client:
+        """Update the client."""
+        path = f"/api/v1/clients/{client.name}"
+        client_update = {
+            "name": client.name,
+            "description": client.description,
+            "public_key": client.public_key,
+        }
+        response = await self._put(path, json=client_update)
+        LOG.info("Response %s", response.text)
+
+        response.raise_for_status()
+        if client.policies:
+            await self.update_client_sources(
+                str(client.id), [str(source) for source in client.policies]
+            )
+        return client
+
+    async def update_client_key(self, client_name: str, public_key: str) -> None:
+        """Update the client key."""
+        path = f"/api/v1/clients/{client_name}/public-key"
+        response = await self._post(path, json={"public_key": public_key})
+
+        response.raise_for_status()
+
+    async def update_client_sources(
+        self, client_name: str, addresses: list[str] | None
+    ) -> None:
+        """Update client source addresses.
+
+        Pass None to sources to allow from all.
+        """
+        if not addresses:
+            addresses = []
+
+        path = f"/api/v1/clients/{client_name}/policies/"
+        response = await self._put(path, json={"sources": addresses})
+
+        response.raise_for_status()
+
+    async def get_detailed_secrets(self) -> list[DetailedSecrets]:
+        """Get detailed list of secrets."""
+        path = "/api/v1/secrets/detailed/"
+        response = await self._get(path)
+        response.raise_for_status()
+
+        secret_list = TypeAdapter(list[DetailedSecrets])
+        return secret_list.validate_python(response.json())
+
+    async def get_secrets(self) -> list[Secret]:
+        """Get Secrets.
+
+        This provides a list of secret names and which clients have them.
+        """
+        path = "/api/v1/secrets/"
+        response = await self._get(path)
+
+        response.raise_for_status()
+
+        secret_list = TypeAdapter(list[Secret])
+        return secret_list.validate_python(response.json())
+
+    async def get_secret(self, name: str) -> Secret | None:
+        """Get clients mapped to a single secret."""
+        path = f"/api/v1/secrets/{name}"
+        response = await self._get(path)
+        if response.status_code == 404:
+            return None
+        response.raise_for_status()
+
+        return Secret.model_validate(response.json())
+
+    async def get_detailed_secret(self, name: str) -> DetailedSecrets | None:
+        """Get clients mapped to a single secret."""
+        path = f"/api/v1/secrets/{name}/detailed"
+        response = await self._get(path)
+        if response.status_code == 404:
+            return None
+        response.raise_for_status()
+
+        return DetailedSecrets.model_validate(response.json())
+
+    async def get_audit_log(
+        self,
+        offset: int = 0,
+        limit: int = 100,
+        client_name: str | None = None,
+        subsystem: str | None = None,
+    ) -> list[AuditLog]:
+        """Get audit log."""
+        path = f"/api/v1/audit/"
+        params: dict[str, str] = {
+            "offset": str(offset),
+            "limit": str(limit),
+        }
+        if client_name:
+            params["filter_client"] = client_name
+
+        if subsystem:
+            params["filter_subsystem"] = subsystem
+
+        response = await self.http_client.get(path, params=params)
+        response.raise_for_status()
+        audit_log_adapter = TypeAdapter(list[AuditLog])
+        return audit_log_adapter.validate_python(response.json())
+
+    async def add_audit_log(self, entry: AuditLog) -> None:
+        """Add audit log entry."""
+        path = f"/api/v1/audit/"
+
+        response = await self.http_client.post(path, json=entry.model_dump())
+        response.raise_for_status()
+
+    async def get_audit_log_count(self) -> int:
+        """Get amount of messages in the audit log."""
+        path = f"/api/v1/audit/info"
+        response = await self._get(path)
+        response.raise_for_status()
+        data = response.json()
+        return int(data["entries"])
+
+    def add_audit_log_sync(self, entry: AuditLog) -> None:
+        """Add audit log entry."""
+        path = f"/api/v1/audit/"
+        LOG.info("AUDIT LOG SYNC %r", entry)
+
+        response = self.sync_client.post(path, json=entry.model_dump())
+        response.raise_for_status()
diff --git a/src/sshecret/backend/exceptions.py b/src/sshecret/backend/exceptions.py
new file mode 100644
index 0000000..f2e8691
--- /dev/null
+++ b/src/sshecret/backend/exceptions.py
@@ -0,0 +1,8 @@
+"""Exceptions."""
+
+class BackendValidationError(Exception):
+    """Validation error."""
+
+
+class BackendConnectionError(Exception):
+    """Could not connect to backend server."""
diff --git a/src/sshecret/backend/models.py b/src/sshecret/backend/models.py
new file mode 100644
index 0000000..9ca4523
--- /dev/null
+++ b/src/sshecret/backend/models.py
@@ -0,0 +1,115 @@
+"""Backend models."""
+
+import enum
+import uuid
+from datetime import datetime
+from typing import Annotated
+
+from pydantic import AfterValidator, BaseModel, IPvAnyAddress, IPvAnyNetwork
+
+from sshecret.crypto import public_key_validator
+
+
+class FilterType(enum.StrEnum):
+    """Type of filter."""
+
+    LIKE = "like"
+    CONTAINS = "contains"
+
+
+class Client(BaseModel):
+    """Implementation of the backend class ClientView."""
+
+    id: uuid.UUID
+    name: str
+    description: str | None
+    public_key: Annotated[str, AfterValidator(public_key_validator)]
+    secrets: list[str]
+    policies: list[IPvAnyNetwork | IPvAnyAddress]
+    created_at: datetime
+    updated_at: datetime | None
+
+
+class ClientQueryResult(BaseModel):
+    """Implementation of the backend ClientQueryResult class."""
+
+    clients: list[Client]
+    total_results: int
+    remaining_results: int
+
+
+class ClientSecret(BaseModel):
+    """Implementation of the backend class ClientSecretResponse."""
+
+    name: str
+    secret: str
+    description: str | None
+    created_at: datetime
+    updated_at: datetime | None
+
+
+class Secret(BaseModel):
+    """Implementation of the backend class ClientSecretList."""
+
+    name: str
+    clients: list[str]
+
+
+class ClientReference(BaseModel):
+    """Implementation of the backend class ClientReference."""
+
+    id: str
+    name: str
+
+
+class DetailedSecrets(BaseModel):
+    """Implementation of the backend class ClientSecretDetailList."""
+
+    name: str
+    ids: list[str]
+    clients: list[ClientReference]
+
+
+class Policy(BaseModel):
+    """Implementation of the backend class ClientPolicyView."""
+
+    sources: list[IPvAnyNetwork | IPvAnyAddress]
+
+
+class ClientFilter(BaseModel):
+    """Client filter."""
+
+    id: str | None = None
+    name: str | None = None
+    filter_name: FilterType | None = None
+
+    def get_params(self) -> dict[str, str]:
+        """Render query parameters."""
+        params: dict[str, str] = {}
+        if not self.id and not self.name:
+            return params
+        if self.id:
+            params["id"] = self.id
+        if self.name and not self.filter_name:
+            params["name"] = self.name
+        elif self.name and self.filter_name is FilterType.LIKE:
+            params["name__like"] = self.name
+        elif self.name and self.filter_name is FilterType.CONTAINS:
+            params["name__contains"] = self.name
+
+        return params
+
+
+class AuditLog(BaseModel):
+    """Implementation of the backend class AuditLog."""
+
+    id: str | None = None
+    subsystem: str | None = None
+    object: str | None = None
+    object_id: str | None = None
+    operation: str
+    client_id: str | None = None
+    client_name: str | None = None
+    message: str
+    origin: str | None = None
+    timestamp: datetime | None = None
diff --git a/src/sshecret/backend/utils.py b/src/sshecret/backend/utils.py
new file mode 100644
index 0000000..df7a4f9
--- /dev/null
+++ b/src/sshecret/backend/utils.py
@@ -0,0 +1,37 @@
+"""Utility functions."""
+
+import logging
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import rsa
+
+
+LOG = logging.getLogger(__name__)
+
+
+def load_public_key(key: bytes | str) -> rsa.RSAPublicKey:
+    if isinstance(key, str):
+        key = key.encode()
+    public_key = serialization.load_ssh_public_key(key)
+    if not isinstance(public_key, rsa.RSAPublicKey):
+        raise ValueError("Only RSA keys are supported.")
+    return public_key
+
+
+def validate_public_key(key: str) -> bool:
+    """Check if key provided in a string is valid."""
+    valid = False
+    public_key: rsa.RSAPublicKey | None = None
+    try:
+        keybytes = key.encode()
+        public_key = load_public_key(keybytes)
+    except Exception as e:
+        LOG.debug("Validation of public key failed: %s", e, exc_info=True)
+    else:
+        valid = True
+
+    if not isinstance(public_key, rsa.RSAPublicKey):
+        valid = False
+
+    if not valid:
+        raise ValueError("Invalid public key. Must an OpenSSH RSA public key.")
+    return valid
diff --git a/src/sshecret/crypto.py b/src/sshecret/crypto.py
new file mode 100644
index 0000000..76f602d
--- /dev/null
+++ b/src/sshecret/crypto.py
@@ -0,0 +1,137 @@
+"""Encryption related functions.
+
+Note! Encryption uses the less secure PKCS1v15 padding. This is to allow
+decryption via openssl on the command line.
+
+"""
+
+import base64
+import logging
+from pathlib import Path
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import rsa
+from cryptography.hazmat.primitives.asymmetric import padding
+
+
+RSA_PUBLIC_EXPONENT = 65537
+RSA_KEY_SIZE = 2048
+
+LOG = logging.getLogger(__name__)
+
+
+def load_public_key(keybytes: bytes) -> rsa.RSAPublicKey:
+    public_key = serialization.load_ssh_public_key(keybytes)
+    if not isinstance(public_key, rsa.RSAPublicKey):
+        raise RuntimeError("Only RSA keys are supported.")
+    return public_key
+
+
+def public_key_validator(public_key: str) -> str:
+    """Validator for public key."""
+    if validate_public_key(public_key):
+        return public_key
+
+    raise ValueError("Error: Public key is not a valid SSH RSA Public Key.")
+
+
+def validate_public_key(key: str) -> bool:
+    """Check if key provided in a string is valid."""
+    valid = False
+    public_key: rsa.RSAPublicKey | None = None
+    try:
+        keybytes = key.encode()
+        public_key = load_public_key(keybytes)
+    except Exception as e:
+        LOG.debug("Validation of public key failed: %s", e, exc_info=True)
+    else:
+        valid = True
+
+    if not isinstance(public_key, rsa.RSAPublicKey):
+        valid = False
+
+    return valid
+
+
+def load_private_key(filename: str, password: str | None = None) -> rsa.RSAPrivateKey:
+    """Load a private key."""
+    password_bytes: bytes | None = None
+    if password:
+        password_bytes = password.encode()
+    with open(filename, "rb") as f:
+        private_key = serialization.load_ssh_private_key(
+            f.read(), password=password_bytes
+        )
+    if not isinstance(private_key, rsa.RSAPrivateKey):
+        raise RuntimeError("Only RSA keys are supported.")
+    return private_key
+
+
+def encrypt_string(string: str, public_key: rsa.RSAPublicKey) -> str:
+    """Encrypt string, end return it base64 encoded."""
+    message = string.encode()
+    ciphertext = public_key.encrypt(
+        message,
+        padding.PKCS1v15(),
+    )
+    return base64.b64encode(ciphertext).decode()
+
+
+def decode_string(ciphertext: str, private_key: rsa.RSAPrivateKey) -> str:
+    """Decode a string. String must be base64 encoded."""
+    decoded = base64.b64decode(ciphertext)
+    decrypted = private_key.decrypt(
+        decoded,
+        padding.PKCS1v15(),
+    )
+    return decrypted.decode()
+
+
+def generate_private_key() -> rsa.RSAPrivateKey:
+    """Generate private RSA key."""
+    private_key = rsa.generate_private_key(
+        public_exponent=RSA_PUBLIC_EXPONENT, key_size=RSA_KEY_SIZE
+    )
+    return private_key
+
+
+def generate_pem(private_key: rsa.RSAPrivateKey) -> str:
+    """Generate PEM."""
+    pem = private_key.private_bytes(
+        encoding=serialization.Encoding.PEM,
+        format=serialization.PrivateFormat.OpenSSH,
+        encryption_algorithm=serialization.NoEncryption(),
+    )
+    return pem.decode()
+
+
+def create_private_rsa_key(filename: Path, password: str | None = None) -> None:
+    """Create an RSA Private key at the given path.
+
+    A password may be provided for secure storage.
+    """
+    if filename.exists():
+        raise RuntimeError("Error: private key file already exists.")
+    LOG.debug("Generating private RSA key at %s", filename)
+    private_key = generate_private_key()
+    encryption_algorithm = serialization.NoEncryption()
+    if password:
+        password_bytes = password.encode()
+        encryption_algorithm = serialization.BestAvailableEncryption(password_bytes)
+    with open(filename, "wb") as f:
+        pem = private_key.private_bytes(
+            encoding=serialization.Encoding.PEM,
+            format=serialization.PrivateFormat.OpenSSH,
+            encryption_algorithm=encryption_algorithm,
+        )
+        lines = f.write(pem)
+        LOG.debug("Wrote %s lines", lines)
+        f.flush()
+
+
+def generate_public_key_string(public_key: rsa.RSAPublicKey) -> str:
+    """Generate public key string."""
+    keybytes = public_key.public_bytes(
+        encoding=serialization.Encoding.OpenSSH,
+        format=serialization.PublicFormat.OpenSSH,
+    )
+    return keybytes.decode()
diff --git a/src/sshecret/settings.py b/src/sshecret/settings.py
new file mode 100644
index 0000000..ef21445
--- /dev/null
+++ b/src/sshecret/settings.py
@@ -0,0 +1,57 @@
+"""Settings management."""
+
+from typing import Literal
+from pydantic import AnyHttpUrl, BaseModel, Field
+
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+DEFAULT_SSH_PORT = 2222
+DEFAULT_BACKEND_PORT = 8822
+DEFAULT_ADMIN_PORT = 8022
+
+
+class SshdSettings(BaseModel):
+    """Settings for the SSHd server."""
+
+    name: Literal["sshd"]
+    listen_address: str = ""
+    backend_token: str
+    port: int = DEFAULT_SSH_PORT
+
+
+class AdminSettings(BaseModel):
+    """Settings for the Admin module."""
+
+    name: Literal["admin"]
+    listen_address: str = ""
+    backend_token: str
+    port: int = DEFAULT_ADMIN_PORT
+
+
+class BackendSettings(BaseModel):
+    """Settings for the backend server."""
+
+    name: Literal["backend"]
+    listen_address: str = ""
+    backend_token: str
+    port: int = DEFAULT_BACKEND_PORT
+
+
+class SshecretSettings(BaseSettings):
+    """General settings model.
+
+    Should probably be subclassed.
+    """
+
+    model_config = SettingsConfigDict(
+        env_prefix="sshecret_",
+        env_nested_delimiter="__",
+        nested_model_default_partial_update=True,
+    )
+
+    backend_url: AnyHttpUrl
+    # This is set up deliberately so only one app can run at the time.
+    application: SshdSettings | AdminSettings | BackendSettings = Field(
+        discriminator="name"
+    )
diff --git a/src/sshecret/testing.py b/src/sshecret/testing.py
new file mode 100644
index 0000000..4eadc35
--- /dev/null
+++ b/src/sshecret/testing.py
@@ -0,0 +1,97 @@
+"""Testing classes."""
+
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import cast
+
+import asyncssh
+import httpx
+
+
+@dataclass
+class BackendContext:
+    """Backend context."""
+
+    url: str
+    token: str
+
+    @property
+    def headers(self) -> dict[str, str]:
+        """Get headers."""
+        return {
+            "X-API-Token": self.token,
+        }
+
+    def test_client(self) -> httpx.AsyncClient:
+        """Create a test client."""
+        return httpx.AsyncClient(base_url=self.url, headers=self.headers)
+
+
+@dataclass
+class AdminContext:
+    """Admin context."""
+
+    url: str
+    username: str = "test"
+    password: str = "test"
+    jwt_token: str | None = field(init=False)
+
+    async def login(self) -> None:
+        """Login to the application."""
+        client = httpx.AsyncClient(base_url=self.url)
+        response = await client.post(
+            "/api/v1/token", data={"username": self.username, "password": self.password}
+        )
+        assert response.status_code == 200
+        token_data = response.json()
+        access_token = cast(str, token_data["access_token"])
+        self.jwt_token = str(access_token)
+
+    @property
+    def headers(self) -> dict[str, str]:
+        """Return headers."""
+        headers: dict[str, str] = {}
+        if self.jwt_token:
+            headers = {"Authorization": f"Bearer {self.jwt_token}"}
+
+        return headers
+
+    def test_client(self) -> httpx.AsyncClient:
+        """Create a test client."""
+        return httpx.AsyncClient(base_url=self.url, headers=self.headers)
+
+
+@dataclass
+class SshServerContext:
+    """SSH server context."""
+
+    host: str
+    port: int
+
+    async def run_command(
+        self, username: str, private_key_file: Path | None, command: str
+    ) -> str:
+        """Run command."""
+        async with self.connect(username, private_key_file) as conn:
+            result = await conn.run(command)
+            assert result.stdout is not None
+            return str(result.stdout.rstrip())
+
+    @asynccontextmanager
+    async def connect(
+        self, username: str, private_key_file: Path | None
+    ) -> AsyncIterator[asyncssh.SSHClientConnection]:
+        """Connect to the server and yield a connection."""
+        private_keys: list[str] = []
+        if private_key_file:
+            private_keys.append(str(private_key_file.absolute()))
+        async with asyncssh.connect(
+            self.host,
+            port=self.port,
+            username=username,
+            known_hosts=None,
+            client_keys=private_keys,
+        ) as conn:
+            yield conn