Validate Sufficient Scope
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Validate Sufficient Scope Wwivw
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π¨βπΌ Some users are authenticating with no scopes which results in having a valid token, but not enough permissions to actually do anything useful with the MCP server. It would be better if we could let them know up front that they don't have enough permissions and need a new token with the appropriate scopes.
To do this, you return a
403 Forbidden response with the appropriate WWW-Authenticate header:// A music streaming app might check scopes like this
const requiredScopes = ['music:read', 'playlists:write']
const userScopes = ['music:read'] // User only has read access
const hasRequiredScopes = requiredScopes.every((scope) =>
userScopes.includes(scope),
)
if (!hasRequiredScopes) {
return new Response('Forbidden', {
status: 403,
headers: {
'WWW-Authenticate': [
`Bearer realm="MusicApp"`,
`error="insufficient_scope"`,
`scopes="${requiredScopes.join(' ')}"`,
].join(', '),
},
})
}
The
WWW-Authenticate header includes:- The realm (
MusicApp) - The error type (
insufficient_scope) - The required scopes (
music:read playlists:write)
However, the
scopes auth param is tricky for us because there's actually a list of valid scope combinations that are allowed. The user could have one of several scopes that would be enough to use the MCP server. There's not an established pattern for handling this case, so we'll skip the scopes auth param and instead include a error_description that explains what scope combinations are valid.π For more details on OAuth scope validation and error handling, see the
OAuth 2.0 Authorization Framework
RFC and OAuth 2.0 Bearer
Token Usage RFC.
π§ββοΈ I created a
minimalValidScopeCombinations array and a hasSufficientScope function for you to use. It's just hard to describe what you should do, but simple once you see it. Feel free to check out my changes if you want.Now, let's implement the scope validation logic to ensure only properly authorized clients can access the EpicMe MCP server!