src/mcp/server/auth/provider.py

from dataclasses import dataclass
from typing import Generic, Literal, Protocol, TypeVar
from urllib.parse import parse_qs, urlencode, urlparse, urlunparse

from pydantic import AnyHttpUrl, BaseModel

from mcp.shared.auth import (
    OAuthClientInformationFull,
    OAuthToken,
)


class AuthorizationParams(BaseModel):
    state: str | None
    scopes: list[str] | None
    code_challenge: str
    redirect_uri: AnyHttpUrl
    redirect_uri_provided_explicitly: bool


class AuthorizationCode(BaseModel):
    code: str
    scopes: list[str]
    expires_at: float
    client_id: str
    code_challenge: str
    redirect_uri: AnyHttpUrl
    redirect_uri_provided_explicitly: bool


class RefreshToken(BaseModel):
    token: str
    client_id: str
    scopes: list[str]
    expires_at: int | None = None


class AccessToken(BaseModel):
    token: str
    client_id: str
    scopes: list[str]
    expires_at: int | None = None


RegistrationErrorCode = Literal[
    "invalid_redirect_uri",
    "invalid_client_metadata",
    "invalid_software_statement",
    "unapproved_software_statement",
]


@dataclass(frozen=True)
class RegistrationError(Exception):
    error: RegistrationErrorCode
    error_description: str | None = None


AuthorizationErrorCode = Literal[
    "invalid_request",
    "unauthorized_client",
    "access_denied",
    "unsupported_response_type",
    "invalid_scope",
    "server_error",
    "temporarily_unavailable",
]


@dataclass(frozen=True)
class AuthorizeError(Exception):
    error: AuthorizationErrorCode
    error_description: str | None = None


TokenErrorCode = Literal[
    "invalid_request",
    "invalid_client",
    "invalid_grant",
    "unauthorized_client",
    "unsupported_grant_type",
    "invalid_scope",
]


@dataclass(frozen=True)
class TokenError(Exception):
    error: TokenErrorCode
    error_description: str | None = None


# NOTE: FastMCP doesn't render any of these types in the user response, so it's
# OK to add fields to subclasses which should not be exposed externally.
AuthorizationCodeT = TypeVar("AuthorizationCodeT", bound=AuthorizationCode)
RefreshTokenT = TypeVar("RefreshTokenT", bound=RefreshToken)
AccessTokenT = TypeVar("AccessTokenT", bound=AccessToken)


class OAuthAuthorizationServerProvider(
    Protocol, Generic[AuthorizationCodeT, RefreshTokenT, AccessTokenT]
):
    async def get_client(self, client_id: str) -> OAuthClientInformationFull | None:
        """
        Retrieves client information by client ID.

        Implementors MAY raise NotImplementedError if dynamic client registration is
        disabled in ClientRegistrationOptions.

        Args:
            client_id: The ID of the client to retrieve.

        Returns:
            The client information, or None if the client does not exist.
        """
        ...

    async def register_client(self, client_info: OAuthClientInformationFull) -> None:
        """
        Saves client information as part of registering it.

        Implementors MAY raise NotImplementedError if dynamic client registration is
        disabled in ClientRegistrationOptions.

        Args:
            client_info: The client metadata to register.

        Raises:
            RegistrationError: If the client metadata is invalid.
        """
        ...

    async def authorize(
        self, client: OAuthClientInformationFull, params: AuthorizationParams
    ) -> str:
        """
        Called as part of the /authorize endpoint, and returns a URL that the client
        will be redirected to.
        Many MCP implementations will redirect to a third-party provider to perform
        a second OAuth exchange with that provider. In this sort of setup, the client
        has an OAuth connection with the MCP server, and the MCP server has an OAuth
        connection with the 3rd-party provider. At the end of this flow, the client
        should be redirected to the redirect_uri from params.redirect_uri.

        +--------+     +------------+     +-------------------+
        |        |     |            |     |                   |
        | Client | --> | MCP Server | --> | 3rd Party OAuth   |
        |        |     |            |     | Server            |
        +--------+     +------------+     +-------------------+
                            |   ^                  |
        +------------+      |   |                  |
        |            |      |   |    Redirect      |
        |redirect_uri|<-----+   +------------------+
        |            |
        +------------+

        Implementations will need to define another handler on the MCP server return
        flow to perform the second redirect, and generate and store an authorization
        code as part of completing the OAuth authorization step.

        Implementations SHOULD generate an authorization code with at least 160 bits of
        entropy,
        and MUST generate an authorization code with at least 128 bits of entropy.
        See https://datatracker.ietf.org/doc/html/rfc6749#section-10.10.

        Args:
            client: The client requesting authorization.
            params: The parameters of the authorization request.

        Returns:
            A URL to redirect the client to for authorization.

        Raises:
            AuthorizeError: If the authorization request is invalid.
        """
        ...

    async def load_authorization_code(
        self, client: OAuthClientInformationFull, authorization_code: str
    ) -> AuthorizationCodeT | None:
        """
        Loads an AuthorizationCode by its code.

        Args:
            client: The client that requested the authorization code.
            authorization_code: The authorization code to get the challenge for.

        Returns:
            The AuthorizationCode, or None if not found
        """
        ...

    async def exchange_authorization_code(
        self, client: OAuthClientInformationFull, authorization_code: AuthorizationCodeT
    ) -> OAuthToken:
        """
        Exchanges an authorization code for an access token and refresh token.

        Args:
            client: The client exchanging the authorization code.
            authorization_code: The authorization code to exchange.

        Returns:
            The OAuth token, containing access and refresh tokens.

        Raises:
            TokenError: If the request is invalid
        """
        ...

    async def load_refresh_token(
        self, client: OAuthClientInformationFull, refresh_token: str
    ) -> RefreshTokenT | None:
        """
        Loads a RefreshToken by its token string.

        Args:
            client: The client that is requesting to load the refresh token.
            refresh_token: The refresh token string to load.

        Returns:
            The RefreshToken object if found, or None if not found.
        """

    ...

    async def exchange_refresh_token(
        self,
        client: OAuthClientInformationFull,
        refresh_token: RefreshTokenT,
        scopes: list[str],
    ) -> OAuthToken:
        """
        Exchanges a refresh token for an access token and refresh token.

        Implementations SHOULD rotate both the access token and refresh token.

        Args:
            client: The client exchanging the refresh token.
            refresh_token: The refresh token to exchange.
            scopes: Optional scopes to request with the new access token.

        Returns:
            The OAuth token, containing access and refresh tokens.

        Raises:
            TokenError: If the request is invalid
        """
        ...

    async def load_access_token(self, token: str) -> AccessTokenT | None:
        """
        Loads an access token by its token.

        Args:
            token: The access token to verify.

        Returns:
            The AuthInfo, or None if the token is invalid.
        """
        ...

    async def revoke_token(
        self,
        token: AccessTokenT | RefreshTokenT,
    ) -> None:
        """
        Revokes an access or refresh token.

        If the given token is invalid or already revoked, this method should do nothing.

        Implementations SHOULD revoke both the access token and its corresponding
        refresh token, regardless of which of the access token or refresh token is
        provided.

        Args:
            token: the token to revoke
        """
        ...


def construct_redirect_uri(redirect_uri_base: str, **params: str | None) -> str:
    parsed_uri = urlparse(redirect_uri_base)
    query_params = [(k, v) for k, vs in parse_qs(parsed_uri.query) for v in vs]
    for k, v in params.items():
        if v is not None:
            query_params.append((k, v))

    redirect_uri = urlunparse(parsed_uri._replace(query=urlencode(query_params)))
    return redirect_uri