verify.ts

import { decode as base64url } from '../../runtime/base64url.ts'
import verify from '../../runtime/verify.ts'

import { JOSEAlgNotAllowed, JWSInvalid, JWSSignatureVerificationFailed } from '../../util/errors.ts'
import { concat, encoder, decoder } from '../../lib/buffer_utils.ts'
import isDisjoint from '../../lib/is_disjoint.ts'
import isObject from '../../lib/is_object.ts'
import checkKeyType from '../../lib/check_key_type.ts'
import validateCrit from '../../lib/validate_crit.ts'
import validateAlgorithms from '../../lib/validate_algorithms.ts'

import type {
  FlattenedVerifyResult,
  KeyLike,
  FlattenedJWSInput,
  JWSHeaderParameters,
  VerifyOptions,
  GetKeyFunction,
  ResolvedKey,
} from '../../types.d.ts'

/**
 * Interface for Flattened JWS Verification dynamic key resolution. No token components have been
 * verified at the time of this function call.
 *
 * @see [createRemoteJWKSet](../functions/jwks_remote.createRemoteJWKSet.md#function-createremotejwkset) to verify using a remote JSON Web Key Set.
 */
export interface FlattenedVerifyGetKey
  extends GetKeyFunction<JWSHeaderParameters | undefined, FlattenedJWSInput> {}

/**
 * Verifies the signature and format of and afterwards decodes the Flattened JWS.
 *
 * @param jws Flattened JWS.
 * @param key Key to verify the JWS with. See
 *   {@link https://github.com/panva/jose/issues/210#jws-alg Algorithm Key Requirements}.
 * @param options JWS Verify options.
 */
export function flattenedVerify(
  jws: FlattenedJWSInput,
  key: KeyLike | Uint8Array,
  options?: VerifyOptions,
): Promise<FlattenedVerifyResult>
/**
 * @param jws Flattened JWS.
 * @param getKey Function resolving a key to verify the JWS with. See
 *   {@link https://github.com/panva/jose/issues/210#jws-alg Algorithm Key Requirements}.
 * @param options JWS Verify options.
 */
export function flattenedVerify<T extends KeyLike = KeyLike>(
  jws: FlattenedJWSInput,
  getKey: FlattenedVerifyGetKey,
  options?: VerifyOptions,
): Promise<FlattenedVerifyResult & ResolvedKey<T>>
export async function flattenedVerify(
  jws: FlattenedJWSInput,
  key: KeyLike | Uint8Array | FlattenedVerifyGetKey,
  options?: VerifyOptions,
) {
  if (!isObject(jws)) {
    throw new JWSInvalid('Flattened JWS must be an object')
  }

  if (jws.protected === undefined && jws.header === undefined) {
    throw new JWSInvalid('Flattened JWS must have either of the "protected" or "header" members')
  }

  if (jws.protected !== undefined && typeof jws.protected !== 'string') {
    throw new JWSInvalid('JWS Protected Header incorrect type')
  }

  if (jws.payload === undefined) {
    throw new JWSInvalid('JWS Payload missing')
  }

  if (typeof jws.signature !== 'string') {
    throw new JWSInvalid('JWS Signature missing or incorrect type')
  }

  if (jws.header !== undefined && !isObject(jws.header)) {
    throw new JWSInvalid('JWS Unprotected Header incorrect type')
  }

  let parsedProt: JWSHeaderParameters = {}
  if (jws.protected) {
    try {
      const protectedHeader = base64url(jws.protected)
      parsedProt = JSON.parse(decoder.decode(protectedHeader))
    } catch {
      throw new JWSInvalid('JWS Protected Header is invalid')
    }
  }
  if (!isDisjoint(parsedProt, jws.header)) {
    throw new JWSInvalid(
      'JWS Protected and JWS Unprotected Header Parameter names must be disjoint',
    )
  }

  const joseHeader: JWSHeaderParameters = {
    ...parsedProt,
    ...jws.header,
  }

  const extensions = validateCrit(
    JWSInvalid,
    new Map([['b64', true]]),
    options?.crit,
    parsedProt,
    joseHeader,
  )

  let b64: boolean = true
  if (extensions.has('b64')) {
    b64 = parsedProt.b64!
    if (typeof b64 !== 'boolean') {
      throw new JWSInvalid(
        'The "b64" (base64url-encode payload) Header Parameter must be a boolean',
      )
    }
  }

  const { alg } = joseHeader

  if (typeof alg !== 'string' || !alg) {
    throw new JWSInvalid('JWS "alg" (Algorithm) Header Parameter missing or invalid')
  }

  const algorithms = options && validateAlgorithms('algorithms', options.algorithms)

  if (algorithms && !algorithms.has(alg)) {
    throw new JOSEAlgNotAllowed('"alg" (Algorithm) Header Parameter not allowed')
  }

  if (b64) {
    if (typeof jws.payload !== 'string') {
      throw new JWSInvalid('JWS Payload must be a string')
    }
  } else if (typeof jws.payload !== 'string' && !(jws.payload instanceof Uint8Array)) {
    throw new JWSInvalid('JWS Payload must be a string or an Uint8Array instance')
  }

  let resolvedKey = false
  if (typeof key === 'function') {
    key = await key(parsedProt, jws)
    resolvedKey = true
  }

  checkKeyType(alg, key, 'verify')

  const data = concat(
    encoder.encode(jws.protected ?? ''),
    encoder.encode('.'),
    typeof jws.payload === 'string' ? encoder.encode(jws.payload) : jws.payload,
  )
  const signature = base64url(jws.signature)
  const verified = await verify(alg, key, signature, data)

  if (!verified) {
    throw new JWSSignatureVerificationFailed()
  }

  let payload: Uint8Array
  if (b64) {
    payload = base64url(jws.payload)
  } else if (typeof jws.payload === 'string') {
    payload = encoder.encode(jws.payload)
  } else {
    payload = jws.payload
  }

  const result: FlattenedVerifyResult = { payload }

  if (jws.protected !== undefined) {
    result.protectedHeader = parsedProt
  }

  if (jws.header !== undefined) {
    result.unprotectedHeader = jws.header
  }

  if (resolvedKey) {
    return { ...result, key }
  }

  return result
}