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fix(passkey): send the PRF extension as binary on login and registration #42

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fix(passkey): send the PRF extension as binary on login and registration #42

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17 changes: 17 additions & 0 deletions frontend/src/app/page.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,22 @@ function bufferToBase64url(buf: ArrayBuffer): string {
return btoa(s).replace(/\+/g, "-").replace(/\//g, "_").replace(/=/g, "");
}

// PRF salts arrive base64url-encoded; WebAuthn expects them as binary.
// Without the PRF extension the server cannot decrypt the IMAP password.
function prepareExtensions(
ext: Record<string, unknown> | undefined,
): AuthenticationExtensionsClientInputs | undefined {
const prf = ext?.prf as
| { evalByCredential?: Record<string, { first: string }> }
| undefined;
if (!prf?.evalByCredential) return undefined;
const byCred: Record<string, { first: ArrayBuffer }> = {};
for (const [credId, values] of Object.entries(prf.evalByCredential)) {
byCred[credId] = { first: base64urlToBuffer(values.first) };
}
return { prf: { evalByCredential: byCred } } as AuthenticationExtensionsClientInputs;
}

function preparePublicKeyOptions(
opts: PasskeyLoginBeginResponse["options"]["publicKey"],
): PublicKeyCredentialRequestOptions {
Expand All @@ -54,6 +70,7 @@ function preparePublicKeyOptions(
})),
userVerification:
(opts.userVerification as UserVerificationRequirement) ?? "required",
extensions: prepareExtensions(opts.extensions),
};
}

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14 changes: 13 additions & 1 deletion frontend/src/components/settings/SecuritySettings.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,18 @@ function bufferToBase64url(buf: ArrayBuffer): string {
return btoa(s).replace(/\+/g, "-").replace(/\//g, "_").replace(/=/g, "");
}

// PRF salt arrives base64url-encoded; WebAuthn expects it as binary.
function prepareExtensions(
ext: Record<string, unknown> | undefined,
): AuthenticationExtensionsClientInputs | undefined {
const prf = ext?.prf as { eval?: { first: string } } | undefined;
if (!prf?.eval) return ext as AuthenticationExtensionsClientInputs | undefined;
return {
...ext,
prf: { eval: { first: base64urlToBuffer(prf.eval.first) } },
} as AuthenticationExtensionsClientInputs;
}

function prepareCreationOptions(
opts: PasskeyRegisterBeginResponse["options"]["publicKey"],
): PublicKeyCredentialCreationOptions {
Expand All @@ -82,7 +94,7 @@ function prepareCreationOptions(
})),
authenticatorSelection: opts.authenticatorSelection as AuthenticatorSelectionCriteria | undefined,
attestation: opts.attestation as AttestationConveyancePreference | undefined,
extensions: opts.extensions,
extensions: prepareExtensions(opts.extensions),
};
}

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