8ad80dd0b4
## Motivation and Context `ClientCredentialsProvider` builds a fixed `client_credentials` token request: `grant_type`, `scope`, `resource`, and the client authentication that `Flow#post_to_token_endpoint` adds. An authorization server that requires further parameters, such as Auth0's `audience`, cannot be used through `oauth:` at all, and giving up `oauth:` also gives up the bearer header and the 401-driven retry that the transport provides. RFC 6749 Section 8.2 allows extension parameters on the token request, and the TypeScript SDK lets a provider shape its token request through `prepareTokenRequest`. `ClientCredentialsProvider.new` now takes `token_request_params:`, a Hash of String keys and values added to every token request the provider makes, and `Flow#post_to_token_endpoint` reads the same name by duck typing, so a `Provider` or `CrossAppAccessProvider` subclass that defines the method gets the same treatment on its authorization code exchange, refresh, or `jwt-bearer` request. `Provider.new` and `CrossAppAccessProvider.new` take the same keyword, held by `StorageBackedProvider` like `authorization_request_validator`, so every bundled provider refuses a bad value before anything is stored. The parameters go underneath the flow's own, so the SDK's values always win, and a key the SDK sets itself (`Flow::RESERVED_TOKEN_REQUEST_PARAMS`) is refused rather than silently overridden: with `ArgumentError` from the constructor, before any `client_information` is written, and again with `ArgumentError` from the flow, before the token request is sent. Only Strings are accepted because `URI.encode_www_form` encodes other scalars and Arrays in ways the caller did not write, and the provider keeps a frozen copy so a later change to the caller's Hash cannot alter what is sent. A Hash comparing keys by identity is refused too, since two equal keys are two entries there, sent twice by a provider method or silently collapsed into one by the copy. The flow raises `ArgumentError` rather than `AuthorizationError` because `MCP::Client::HTTP` treats a failed refresh as a reason to run the interactive flow, which would then fail the same way after the user signed in. Both refusals raise `Flow::InvalidTokenRequestParamsError`, a subclass of `ArgumentError`, so a caller can tell them from an unknown keyword, and the copy duplicates keys as well as values, since `Hash` copies only keys whose class is exactly `String`. Fixes #554. ## How Has This Been Tested? New tests cover every token request the parameters can ride (the `client_credentials` grant under all three client authentication methods, the authorization code exchange, refresh, and `jwt-bearer`), both refusal boundaries (the constructors of all three providers, and the flow for a provider defining the method), and the transport surfacing a refused hook from a refresh attempt without starting the interactive flow. All of them fail against the previous library. ## Breaking Changes None. The keyword is optional and the hook is opt-in; a provider that does not define `token_request_params` sends the same requests as before.
72 lines
3.1 KiB
Ruby
72 lines
3.1 KiB
Ruby
# frozen_string_literal: true
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module MCP
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class Client
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module OAuth
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# Shared token/credential persistence for the OAuth provider classes
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# (`Provider` for the authorization-code flow, `ClientCredentialsProvider`
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# for the client_credentials flow, and `CrossAppAccessProvider` for the jwt-bearer flow).
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# The grants differ in how they authenticate, but all read and write the same two pieces of state
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# through a `storage` object: the token response and the client information. This module supplies
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# that delegation so the `Flow` orchestrator can treat any provider uniformly.
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#
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# Including classes must set `@storage` to an object responding to `tokens`,
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# `save_tokens(tokens)`, `client_information`, and `save_client_information(info)`
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# (see `InMemoryStorage`).
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module StorageBackedProvider
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# Optional `->(request) { true | false }` hook, called with an `AuthorizationRequest`.
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# An MCP server names its own authorization server and the scopes to ask for, so this is where
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# an embedding application sees both before the request is made and can decline to proceed.
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# `nil` (the default) authorizes whatever the server asked for, which is the behavior every
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# MCP SDK has today.
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attr_reader :authorization_request_validator
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# Optional Hash of String keys and values added to every token request the provider makes, for parameters
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# the authorization server requires beyond the grant itself (RFC 6749 Section 8.2 leaves room for them;
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# Auth0's `audience` is the usual one). `nil` (the default) adds nothing.
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# Set through `frozen_token_request_params`, which refuses a key `Flow` sets itself or a wrongly shaped value
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# with `Flow::InvalidTokenRequestParamsError`.
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attr_reader :token_request_params
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def access_token
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tokens&.dig("access_token") || tokens&.dig(:access_token)
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end
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def tokens
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@storage.tokens
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end
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def save_tokens(tokens)
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@storage.save_tokens(tokens)
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end
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def client_information
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@storage.client_information
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end
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def save_client_information(info)
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@storage.save_client_information(info)
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end
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def clear_tokens!
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@storage.save_tokens(nil)
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end
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private
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# Constructors call this before writing to `storage`, so a rejected provider leaves it untouched.
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# The copy has its own frozen keys and values, so a later change to the caller's Hash, to a key,
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# or to a value cannot alter what is sent to the token endpoint. Keys are copied explicitly
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# because `Hash` copies and freezes only keys whose class is exactly `String`.
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def frozen_token_request_params(params)
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return if params.nil?
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problem = Flow.token_request_params_problem(params)
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raise Flow::InvalidTokenRequestParamsError, "token_request_params #{problem}" if problem
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params.each_with_object({}) { |(key, value), copy| copy[key.dup.freeze] = value.dup.freeze }.freeze
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end
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end
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end
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end
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end
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