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28877fade9
The final part (for now) of my work to implement a username picker in synapse itself. The idea is that we allow `UsernameMappingProvider`s to return `localpart=None`, in which case, rather than redirecting the browser back to the client, we redirect to a username-picker resource, which allows the user to enter a username. We *then* complete the SSO flow (including doing the client permission checks). The static resources for the username picker itself (in https://github.com/matrix-org/synapse/tree/rav/username_picker/synapse/res/username_picker) are essentially lifted wholesale from https://github.com/matrix-org/matrix-synapse-saml-mozilla/tree/master/matrix_synapse_saml_mozilla/res. As the comment says, we might want to think about making them customisable, but that can be a follow-up. Fixes #8876.
193 lines
10 KiB
Markdown
193 lines
10 KiB
Markdown
# SSO Mapping Providers
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A mapping provider is a Python class (loaded via a Python module) that
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works out how to map attributes of a SSO response to Matrix-specific
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user attributes. Details such as user ID localpart, displayname, and even avatar
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URLs are all things that can be mapped from talking to a SSO service.
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As an example, a SSO service may return the email address
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"john.smith@example.com" for a user, whereas Synapse will need to figure out how
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to turn that into a displayname when creating a Matrix user for this individual.
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It may choose `John Smith`, or `Smith, John [Example.com]` or any number of
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variations. As each Synapse configuration may want something different, this is
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where SAML mapping providers come into play.
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SSO mapping providers are currently supported for OpenID and SAML SSO
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configurations. Please see the details below for how to implement your own.
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It is up to the mapping provider whether the user should be assigned a predefined
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Matrix ID based on the SSO attributes, or if the user should be allowed to
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choose their own username.
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In the first case - where users are automatically allocated a Matrix ID - it is
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the responsibility of the mapping provider to normalise the SSO attributes and
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map them to a valid Matrix ID. The [specification for Matrix
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IDs](https://matrix.org/docs/spec/appendices#user-identifiers) has some
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information about what is considered valid.
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If the mapping provider does not assign a Matrix ID, then Synapse will
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automatically serve an HTML page allowing the user to pick their own username.
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External mapping providers are provided to Synapse in the form of an external
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Python module. You can retrieve this module from [PyPI](https://pypi.org) or elsewhere,
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but it must be importable via Synapse (e.g. it must be in the same virtualenv
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as Synapse). The Synapse config is then modified to point to the mapping provider
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(and optionally provide additional configuration for it).
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## OpenID Mapping Providers
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The OpenID mapping provider can be customized by editing the
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`oidc_config.user_mapping_provider.module` config option.
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`oidc_config.user_mapping_provider.config` allows you to provide custom
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configuration options to the module. Check with the module's documentation for
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what options it provides (if any). The options listed by default are for the
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user mapping provider built in to Synapse. If using a custom module, you should
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comment these options out and use those specified by the module instead.
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### Building a Custom OpenID Mapping Provider
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A custom mapping provider must specify the following methods:
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* `__init__(self, parsed_config)`
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- Arguments:
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- `parsed_config` - A configuration object that is the return value of the
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`parse_config` method. You should set any configuration options needed by
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the module here.
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* `parse_config(config)`
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- This method should have the `@staticmethod` decoration.
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- Arguments:
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- `config` - A `dict` representing the parsed content of the
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`oidc_config.user_mapping_provider.config` homeserver config option.
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Runs on homeserver startup. Providers should extract and validate
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any option values they need here.
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- Whatever is returned will be passed back to the user mapping provider module's
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`__init__` method during construction.
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* `get_remote_user_id(self, userinfo)`
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- Arguments:
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- `userinfo` - A `authlib.oidc.core.claims.UserInfo` object to extract user
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information from.
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- This method must return a string, which is the unique identifier for the
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user. Commonly the ``sub`` claim of the response.
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* `map_user_attributes(self, userinfo, token, failures)`
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- This method must be async.
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- Arguments:
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- `userinfo` - A `authlib.oidc.core.claims.UserInfo` object to extract user
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information from.
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- `token` - A dictionary which includes information necessary to make
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further requests to the OpenID provider.
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- `failures` - An `int` that represents the amount of times the returned
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mxid localpart mapping has failed. This should be used
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to create a deduplicated mxid localpart which should be
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returned instead. For example, if this method returns
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`john.doe` as the value of `localpart` in the returned
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dict, and that is already taken on the homeserver, this
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method will be called again with the same parameters but
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with failures=1. The method should then return a different
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`localpart` value, such as `john.doe1`.
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- Returns a dictionary with two keys:
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- `localpart`: A string, used to generate the Matrix ID. If this is
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`None`, the user is prompted to pick their own username.
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- `displayname`: An optional string, the display name for the user.
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* `get_extra_attributes(self, userinfo, token)`
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- This method must be async.
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- Arguments:
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- `userinfo` - A `authlib.oidc.core.claims.UserInfo` object to extract user
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information from.
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- `token` - A dictionary which includes information necessary to make
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further requests to the OpenID provider.
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- Returns a dictionary that is suitable to be serialized to JSON. This
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will be returned as part of the response during a successful login.
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Note that care should be taken to not overwrite any of the parameters
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usually returned as part of the [login response](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-login).
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### Default OpenID Mapping Provider
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Synapse has a built-in OpenID mapping provider if a custom provider isn't
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specified in the config. It is located at
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[`synapse.handlers.oidc_handler.JinjaOidcMappingProvider`](../synapse/handlers/oidc_handler.py).
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## SAML Mapping Providers
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The SAML mapping provider can be customized by editing the
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`saml2_config.user_mapping_provider.module` config option.
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`saml2_config.user_mapping_provider.config` allows you to provide custom
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configuration options to the module. Check with the module's documentation for
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what options it provides (if any). The options listed by default are for the
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user mapping provider built in to Synapse. If using a custom module, you should
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comment these options out and use those specified by the module instead.
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### Building a Custom SAML Mapping Provider
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A custom mapping provider must specify the following methods:
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* `__init__(self, parsed_config, module_api)`
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- Arguments:
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- `parsed_config` - A configuration object that is the return value of the
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`parse_config` method. You should set any configuration options needed by
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the module here.
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- `module_api` - a `synapse.module_api.ModuleApi` object which provides the
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stable API available for extension modules.
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* `parse_config(config)`
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- This method should have the `@staticmethod` decoration.
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- Arguments:
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- `config` - A `dict` representing the parsed content of the
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`saml_config.user_mapping_provider.config` homeserver config option.
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Runs on homeserver startup. Providers should extract and validate
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any option values they need here.
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- Whatever is returned will be passed back to the user mapping provider module's
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`__init__` method during construction.
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* `get_saml_attributes(config)`
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- This method should have the `@staticmethod` decoration.
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- Arguments:
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- `config` - A object resulting from a call to `parse_config`.
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- Returns a tuple of two sets. The first set equates to the SAML auth
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response attributes that are required for the module to function, whereas
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the second set consists of those attributes which can be used if available,
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but are not necessary.
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* `get_remote_user_id(self, saml_response, client_redirect_url)`
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- Arguments:
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- `saml_response` - A `saml2.response.AuthnResponse` object to extract user
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information from.
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- `client_redirect_url` - A string, the URL that the client will be
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redirected to.
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- This method must return a string, which is the unique identifier for the
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user. Commonly the ``uid`` claim of the response.
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* `saml_response_to_user_attributes(self, saml_response, failures, client_redirect_url)`
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- Arguments:
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- `saml_response` - A `saml2.response.AuthnResponse` object to extract user
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information from.
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- `failures` - An `int` that represents the amount of times the returned
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mxid localpart mapping has failed. This should be used
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to create a deduplicated mxid localpart which should be
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returned instead. For example, if this method returns
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`john.doe` as the value of `mxid_localpart` in the returned
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dict, and that is already taken on the homeserver, this
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method will be called again with the same parameters but
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with failures=1. The method should then return a different
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`mxid_localpart` value, such as `john.doe1`.
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- `client_redirect_url` - A string, the URL that the client will be
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redirected to.
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- This method must return a dictionary, which will then be used by Synapse
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to build a new user. The following keys are allowed:
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* `mxid_localpart` - The mxid localpart of the new user. If this is
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`None`, the user is prompted to pick their own username.
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* `displayname` - The displayname of the new user. If not provided, will default to
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the value of `mxid_localpart`.
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* `emails` - A list of emails for the new user. If not provided, will
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default to an empty list.
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Alternatively it can raise a `synapse.api.errors.RedirectException` to
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redirect the user to another page. This is useful to prompt the user for
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additional information, e.g. if you want them to provide their own username.
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It is the responsibility of the mapping provider to either redirect back
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to `client_redirect_url` (including any additional information) or to
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complete registration using methods from the `ModuleApi`.
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### Default SAML Mapping Provider
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Synapse has a built-in SAML mapping provider if a custom provider isn't
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specified in the config. It is located at
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[`synapse.handlers.saml_handler.DefaultSamlMappingProvider`](../synapse/handlers/saml_handler.py).
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