11-25-2025 compliant Auth by wdawson · Pull Request #651 · modelcontextprotocol/rust-sdk

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawson · 2026-02-10T00:31:56Z

Bring the SDK's OAuth implementation into compliance with MCP Authorization Spec 2025-11-25 and wire up automatic scope selection and upgrade flows.

As discussed with @alexhancock in #641

Motivation and Context

The SDK's OAuth implementation targeted the 2025-03-26 spec and was missing several features from the 2025-11-25 revision:

RFC 8707 resource parameter binding (MUST per spec)
PKCE S256 support verification against server metadata
WWW-Authenticate error/error_description parsing
Scope selection priority (WWW-Authenticate > PRM > AS metadata > defaults)
403 insufficient_scope handling and step-up authorization (SEP-835)
Protected Resource Metadata scopes_supported (RFC 9728)

SDK consumers also had to manually manage scope selection and handle scope upgrade flows. This change makes those automatic.

How Has This Been Tested?

42 auth-specific unit tests covering header parsing, server validation, scope union, upgrade tracking, authorization URL generation, and state store operations
All 132 rmcp lib unit tests pass (cargo test -p rmcp --lib --all-features)
Server and client examples build cleanly
Not yet tested end-to-end against a live server (@alexhancock offered to do this)

Breaking Changes

AuthorizationMetadata has a new field code_challenge_methods_supported: Option<Vec<String>>. Code that constructs this struct with explicit fields (not ..Default::default()) will need to add the field. The complex_auth_streamhttp example has been updated accordingly.
handle_response() now returns AuthError::InsufficientScope on 403 with error="insufficient_scope" in the WWW-Authenticate header, and AuthError::AuthorizationFailed("Forbidden") for other 403 responses. Previously all non-401 responses were passed through as Ok.

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

This incorporates work from PR #595 by @fizy069 (SEP-835 scope handling). The relevant commits include a Co-authored-by trailer to preserve attribution.

Security vs compatibility philosophy: the SDK defaults to correct spec behavior but falls back gracefully for non-compliant servers, except where the fallback would be insecure. PKCE S256 is always enforced (never falls back to plain or no challenge). RFC 8707 resource parameter is always sent but the flow continues if the server ignores it.

The select_scopes() priority chain follows SEP-835:

scope from WWW-Authenticate header
scopes_supported from Protected Resource Metadata (RFC 9728)
scopes_supported from AS metadata
Caller-provided defaults

Passing empty scopes to start_authorization() triggers auto-selection using this chain.

- add WWWAuthenticateParams for parsing scope and resource_metadata from headers - add ScopeUpgradeConfig and scope tracking in AuthorizationManager - add InsufficientScopeError and 403 handling in streamable HTTP client - add scope union computation for progressive authorization - export new public types: AuthClient, ScopeUpgradeConfig, WWWAuthenticateParams Co-authored-by: fizy069 <fizy069@users.noreply.github.com>

nbarbettini · 2026-02-10T01:16:51Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

wdawson · 2026-02-11T00:30:07Z

Idea: conformance could be used to test against a live server. Some of the other SDK projects test against it in CI, e.g. https://github.com/modelcontextprotocol/python-sdk/blob/main/.github/workflows/conformance.yml

Will leave this up to @alexhancock to tackle in a separate PR probably. Unless you'd like me to add here. Don't want it to be bigger than it needs to be

alexhancock · 2026-02-12T16:30:35Z

Nice @wdawson. Thanks! Will get it released soon

wdawsonand others added 10 commits February 4, 2026 15:06

fix: correct discovery for AS metadata
0da5e6a

fix: add commitlint to dev container
d406332

feat: add RFC 8707 support for resource parameter
314d1b0

feat: pkce method verification
d703a3e

fix: reorg auth tests
80379ed

feat: add error to www-authenticate header parsing
c80bfa9

feat: consider protected resource metadata in scope selection
c18ad44

fix: reorganize auth tests
7a96e4e

feat: add examples and docs for updated auth
119c0bc

github-actionsBot added T-documentation Documentation improvements T-config Configuration file changes T-core Core library changes T-examples Example code changes T-transport Transport layer changes labels Feb 10, 2026

alexhancock mentioned this pull request Feb 12, 2026
feat(auth): add token_endpoint_auth_method to OAuthClientConfig #648
Merged
9 tasks

alexhancock self-requested a review February 12, 2026 15:12

alexhancock approved these changes Feb 12, 2026
View reviewed changes

alexhancock merged commit 61845d6 into modelcontextprotocol:mainFeb 12, 2026
11 checks passed

github-actionsBot mentioned this pull request Feb 12, 2026
chore: release v0.16.0 #652
Merged

wdawson deleted the feat/auth branch February 12, 2026 17:42

wdawson mentioned this pull request Feb 12, 2026
Implementation of SEP835 : Scope parameter parsing from WWW-Authenticate headers #595
Closed
6 tasks

ekarcnevets mentioned this pull request Feb 17, 2026
MCP OAuth login fails for Kapa-hosted Strapi docs server unless authorize URL includes resource parameter openai/codex#11292
Closed

glicht mentioned this pull request Feb 22, 2026
fix(auth): current_scopes read to async #678
Merged
9 tasks

mishapavlov1 mentioned this pull request Feb 23, 2026
Codex mcp login fails with OAuth providers that require resource (eg. MarketingCloud MCP) openai/codex#12589
Closed

This was referenced Mar 31, 2026
pull in remote fixes for oauth warpdotdev/rmcp#8
Closed
Fixes for oauth expiry and scopes warpdotdev/rmcp#9
Merged

This was referenced Apr 29, 2026
feat(auth): add RFC 8707 resource parameter to authorize and token requests warpdotdev/rmcp#10
Open
Atlassian MCP server OAuth login fails: rmcp omits RFC 8707 resource parameter from /authorize and /token warpdotdev/warp#9462
Open