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Handle validation and mapping of PRF inputs to client
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,199 @@ | ||
| use std::collections::HashMap; | ||
|
|
||
| use passkey_types::{ | ||
| crypto::sha256, | ||
| ctap2::{ | ||
| extensions::{AuthenticatorPrfInputs, AuthenticatorPrfValues}, | ||
| get_assertion, get_info, make_credential, | ||
| }, | ||
| webauthn::{ | ||
| AuthenticationExtensionsClientInputs, AuthenticationExtensionsPrfInputs, | ||
| AuthenticationExtensionsPrfValues, PublicKeyCredentialDescriptor, | ||
| PublicKeyCredentialRequestOptions, | ||
| }, | ||
| Bytes, | ||
| }; | ||
|
|
||
| use crate::WebauthnError; | ||
|
|
||
| type Result<T> = ::std::result::Result<T, WebauthnError>; | ||
|
|
||
| pub(super) fn registration_prf_to_ctap2_input( | ||
| request: Option<&AuthenticationExtensionsClientInputs>, | ||
| supported_extensions: &[get_info::Extension], | ||
| ) -> Result<Option<make_credential::ExtensionInputs>> { | ||
| make_ctap_extension(request.and_then(|r| r.prf.as_ref()), supported_extensions) | ||
| } | ||
|
|
||
| fn validate_no_eval_by_cred( | ||
| prf_input: Option<&AuthenticationExtensionsPrfInputs>, | ||
| ) -> Result<Option<&AuthenticationExtensionsPrfInputs>> { | ||
| Ok(match prf_input { | ||
| Some(prf) if prf.eval_by_credential.is_some() => { | ||
| return Err(WebauthnError::NotSupportedError); | ||
| } | ||
| Some(prf) => Some(prf), | ||
| None => None, | ||
| }) | ||
| } | ||
|
|
||
| fn convert_eval_to_ctap( | ||
| eval: &AuthenticationExtensionsPrfValues, | ||
| ) -> Result<AuthenticatorPrfValues> { | ||
| let (first, second) = { | ||
| let salt1 = make_salt(&eval.first); | ||
| let salt2 = eval.second.as_ref().map(make_salt); | ||
| (salt1, salt2) | ||
| }; | ||
|
|
||
| Ok(AuthenticatorPrfValues { first, second }) | ||
| } | ||
|
|
||
| fn make_ctap_extension( | ||
| prf: Option<&AuthenticationExtensionsPrfInputs>, | ||
| supported_extensions: &[get_info::Extension], | ||
| ) -> Result<Option<make_credential::ExtensionInputs>> { | ||
| // Check if PRF extension input is provided and process it. | ||
| // | ||
| // Should return a "NotSupportedError" if `evalByCredential` is present | ||
| // in this registration request. | ||
| let prf = validate_no_eval_by_cred(prf)?; | ||
|
|
||
| // Only request hmac-secret extension input if it's enabled on the authenticator and prf is requested. | ||
| let hmac_secret = prf.and_then(|_| { | ||
| supported_extensions | ||
| .contains(&get_info::Extension::HmacSecret) | ||
| .then_some(true) | ||
| }); | ||
|
|
||
| let prf = prf | ||
| .filter(|_| supported_extensions.contains(&get_info::Extension::Prf)) | ||
| .map(|prf| { | ||
| // Only create prf extension input if it's enabled on the authenticator. | ||
| prf.eval | ||
| .as_ref() | ||
| .map(convert_eval_to_ctap) | ||
| .transpose() | ||
| .map(|eval| AuthenticatorPrfInputs { | ||
| eval, | ||
| eval_by_credential: None, | ||
| }) | ||
| }) | ||
| .transpose()?; | ||
|
|
||
| // If any of the input fields are Some, only then should this pass | ||
| // a Some(ExtensionInputs) to authenticator. Otherwise, it should | ||
| // forward a None. | ||
| Ok(make_credential::ExtensionInputs { | ||
| hmac_secret, | ||
| hmac_secret_mc: None, | ||
| prf, | ||
| } | ||
| .zip_contents()) | ||
| } | ||
|
|
||
| pub(super) fn auth_prf_to_ctap2_input( | ||
| request: &PublicKeyCredentialRequestOptions, | ||
| supported_extensions: &[get_info::Extension], | ||
| ) -> Result<Option<get_assertion::ExtensionInputs>> { | ||
| get_ctap_extension( | ||
| request.allow_credentials.as_deref(), | ||
| request.extensions.as_ref().and_then(|ext| ext.prf.as_ref()), | ||
| supported_extensions, | ||
| ) | ||
| } | ||
|
|
||
| fn get_ctap_extension( | ||
| allow_credentials: Option<&[PublicKeyCredentialDescriptor]>, | ||
| prf_input: Option<&AuthenticationExtensionsPrfInputs>, | ||
| supported_extensions: &[get_info::Extension], | ||
| ) -> Result<Option<get_assertion::ExtensionInputs>> { | ||
| // Check if the authenticator supports prf before continuing | ||
| if !supported_extensions.contains(&get_info::Extension::Prf) { | ||
| return Ok(None); | ||
| } | ||
| // Check if PRF extension input is provided and process it. | ||
| let eval_by_credential = prf_input | ||
| .as_ref() | ||
| .and_then(|prf| prf.eval_by_credential.as_ref()); | ||
|
|
||
| // If evalByCredential is not empty but allowCredentials is empty, | ||
| // return a DOMException whose name is “NotSupportedError”. | ||
| if eval_by_credential.is_some_and(|record| !record.is_empty()) | ||
| && (allow_credentials.is_none() | ||
| || allow_credentials | ||
| .as_ref() | ||
| .is_some_and(|allow| allow.is_empty())) | ||
| { | ||
| return Err(WebauthnError::NotSupportedError); | ||
| } | ||
|
|
||
| // Pre-compute the parsed values of the base64url-encoded key s.t. we | ||
| // can speed up our logic later on instead of having the re-compute | ||
| // these values there again. | ||
| // TODO: consolidate with authenticator logic | ||
| let precomputed_eval_cred = eval_by_credential | ||
| .map(|record| { | ||
| record | ||
| .iter() | ||
| .map(|(key, val)| { | ||
| Bytes::try_from(key.as_str()) | ||
| .map(|k| (k, val)) | ||
| .map_err(|_| WebauthnError::SyntaxError) | ||
| }) | ||
| .collect::<Result<Vec<_>>>() | ||
| }) | ||
| .transpose()?; | ||
|
|
||
| // If any key in evalByCredential is the empty string, or is not a valid | ||
| // base64url encoding, or does not equal the id of some element of | ||
| // allowCredentials after performing base64url decoding, then return a | ||
| // DOMException whose name is “SyntaxError”. | ||
| if let Some(record) = precomputed_eval_cred.as_ref() { | ||
| if record.iter().any(|(k_bytes, _)| { | ||
| k_bytes.is_empty() | ||
| || allow_credentials | ||
| .as_ref() | ||
| .is_some_and(|allow| !allow.iter().any(|cred| cred.id == *k_bytes)) | ||
| }) { | ||
| return Err(WebauthnError::SyntaxError); | ||
| } | ||
| } | ||
|
|
||
| let new_eval_by_cred = precomputed_eval_cred | ||
| .map(|map| { | ||
| map.into_iter() | ||
| .map(|(k, values)| convert_eval_to_ctap(values).map(|v| (k, v))) | ||
| .collect::<Result<HashMap<_, _>>>() | ||
| }) | ||
| .transpose()?; | ||
|
|
||
| let eval = prf_input | ||
| .and_then(|prf| prf.eval.as_ref().map(convert_eval_to_ctap)) | ||
| .transpose()?; | ||
|
|
||
| let prf = prf_input.map(|_| AuthenticatorPrfInputs { | ||
| eval, | ||
| eval_by_credential: new_eval_by_cred, | ||
| }); | ||
|
|
||
| let extension_inputs = get_assertion::ExtensionInputs { | ||
| hmac_secret: None, | ||
| prf, | ||
| } | ||
| .zip_contents(); | ||
|
|
||
| Ok(extension_inputs) | ||
| } | ||
|
|
||
| // Build the value that's used as salt by the CTAP2 hmac-secret extension. | ||
| fn make_salt(prf_value: &Bytes) -> [u8; 32] { | ||
| sha256( | ||
| &b"WebAuthn PRF" | ||
| .iter() | ||
| .chain(std::iter::once(&0x0)) | ||
| .chain(prf_value) | ||
| .cloned() | ||
| .collect::<Vec<_>>(), | ||
| ) | ||
| } |
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