app/auth/BearerTokenAuth.scala

package auth

import java.time.Instant
import java.util.Date

import com.nimbusds.jose.crypto.RSASSAVerifier
import com.nimbusds.jose.jwk.{JWK, JWKSet}
import com.nimbusds.jwt.{JWTClaimsSet, SignedJWT}
import javax.inject.{Inject, Singleton}
import org.slf4j.LoggerFactory
import play.api.mvc.RequestHeader
import play.api.Configuration
import play.api.libs.typedmap.TypedKey
import java.net.URL
import scala.io.Source
import scala.util.{Failure, Success, Try}

object BearerTokenAuth {
  final val ClaimsAttributeKey = TypedKey[JWTClaimsSet]("claims")
}

/**
 * this class implements bearer token authentication. It's injectable because it needs to access app config.
 * You don't need to integrate it directly in your controller, it is required by the Security trait.
 *
 * This expects there to be an `auth` section in the application.conf which should contain two keys:
 * auth {
 *   adminClaim = "claim-field-indicating-admin"
 *   tokenSigningCert = """----- BEGIN CERTIFICATE -----
 *   {your certificate....}
 *   ----- END CERTIFICATE -----"""
 * }
 *
 * A given bearer token must authenticate against the provided certificate to be allowed access, and its expiry time
 * must not be in the past. The token's subject field ("sub") is used as the username.
 * Admin access is only granted if the token's field given by auth.adminClaim is a string that equates to "true" or "yes".
 *
 * So, in order to use it:
 *
 * class MyController @Inject() (controllerComponents:ControllerComponents, override bearerTokenAuth:BearerTokenAuth) extends AbstractController(controllerComponets) with Security { }
 * @param config application configuration object. This is normally provided by the injector
 */
@Singleton
class BearerTokenAuth @Inject() (config:Configuration) {
  private val logger = LoggerFactory.getLogger(getClass)

  //see https://stackoverflow.com/questions/475074/regex-to-parse-or-validate-base64-data
  //it is not the best option but is the simplest that will work here
  private val authXtractor = "^Bearer\\s+([a-zA-Z0-9+/._-]*={0,3})$".r
  var loadTime: Long = System.currentTimeMillis / 1000
  private var maybeVerifiers = loadInKey() match {
    case Failure(err)=>
      if(!sys.env.contains("CI")) logger.warn(s"No token validation cert in config so bearer token auth will not work. Error was ${err.getMessage}")
      None
    case Success(jwk)=>
      Some(jwk)
  }

  /**
   * returns the configured name for the claim field that will give whether a user is an admin or not.
   * It's included here because the Security trait is a mixin and can't access the config directly.
   * @return
   */
  def isAdminClaimName():String = {
    config.get[String]("auth.adminClaim")
  }

  /**
   * extracts the authorization token from the provided header
   * @param fromString complete Authorization header text
   * @return None if the header text does not match the expected format. The raw bearer token if it does.
   */
  def extractAuthorization(fromString:String):Either[LoginResult,LoginResultOK[String]] =
    fromString match {
      case authXtractor(token)=>
        logger.debug("found valid base64 bearer")
        Right(LoginResultOK(token))
      case _=>
        logger.warn("no bearer token found or it failed to validate")
        Left(LoginResultInvalid("no token"))
    }

  private def signingCertPath = config.get[String]("auth.tokenSigningCertPath")

  protected def loadRemoteJWKSet(remotePath:String) = JWKSet.load(new URL(remotePath))

  protected def loadLocalJWKSet(pemCertLocation:String) = {
    val s = Source.fromFile(pemCertLocation, "UTF-8")
    try {
      val pemCertData = s.getLines().reduce(_ + _)
      new JWKSet(JWK.parseFromPEMEncodedX509Cert(pemCertData))
    } finally {
      s.close()
    }
  }

  /**
   * Loads in the public certificate(s) used for validating the bearer tokens from configuration.
   * @return Either an initialised JWKSet or a Failure indicating why it would not load.
   */
  def loadInKey():Try[JWKSet] = Try {
    loadTime = System.currentTimeMillis / 1000
    val isRemoteMatcher = "^https*:".r.unanchored

    if(isRemoteMatcher.matches(signingCertPath)) {
      logger.info(s"Loading JWKS from $signingCertPath")

      val set = loadRemoteJWKSet(signingCertPath)
      logger.info(s"Loaded in ${set.getKeys.toArray.length} keys from endpoint")
      set
    } else {
      logger.info(s"Loading JWKS from local path $signingCertPath")
      loadLocalJWKSet(signingCertPath)
    }
  }

  def getVerifier(maybeKeyId:Option[String]) = maybeVerifiers match {
    case Some(verifiers) =>
      maybeKeyId match {
        case Some(kid) =>
          logger.info(s"Provided JWT is signed with key ID $kid")
          val list = verifiers.getKeys
          if (list.size > 1) {
            Option(verifiers.getKeyByKeyId(kid))
              .map(jwk=>new RSASSAVerifier(jwk.toRSAKey))
          } else {
            if (list.isEmpty) None else Some(new RSASSAVerifier(list.get(0).toRSAKey))
          }
        case None =>
          logger.info(s"Provided JWT has no key ID, using first available cert")
          val list = verifiers.getKeys
          if (list.isEmpty) None else Some(new RSASSAVerifier(list.get(0).toRSAKey))
      }
    case None=>None
  }

  /**
    * try to validate the given token with the key provided
    * returns a JWTClaimsSet if successful
    * @param token JWT token to verify
    * @return a Try, containing a JWTClaimsSet or an error
    */
  def validateToken(token:LoginResultOK[String]):Either[LoginResult,LoginResultOK[JWTClaimsSet]] = {
    logger.debug(s"validating token $token")
    Try {
      SignedJWT.parse(token.content)
    } match {
      case Success(signedJWT) =>
        if ((System.currentTimeMillis / 1000) - loadTime > config.get[Int]("auth.keyTimeOut")) {
          logger.debug(s"Keys too old. Attempting key refresh.")
          maybeVerifiers = loadInKey() match {
            case Failure(err)=>
              if(!sys.env.contains("CI")) logger.warn(s"Could not load keys. Error was ${err.getMessage}")
              None
            case Success(jwk)=>
              Some(jwk)
          }
        }
        getVerifier(Option(signedJWT.getHeader.getKeyID)) match {
          case Some(verifier)=>
            if (signedJWT.verify(verifier)) {
              logger.debug("verified JWT")
              logger.debug(s"${signedJWT.getJWTClaimsSet.toJSONObject(true).toString}")
              Right(LoginResultOK(signedJWT.getJWTClaimsSet))
            } else {
              Left(LoginResultInvalid(token.content))
            }
          case None =>
            logger.error(s"No signing certificate could be found. There are ${maybeVerifiers.map(_.getKeys.toArray.length).getOrElse(0)} configured keys from location '$signingCertPath'")
            Left(LoginResultMisconfigured("No signing cert configured"))
        }
      case Failure(err) =>
        logger.error(s"Failed to validate token for ${token.content}: ${err.getMessage}")
        Left(LoginResultInvalid(token.content))
    }
  }

  /**
   * check the given parsed claims set to see if the token has already expired
   * @param claims JWTClaimsSet representing the token under consideration
   * @return a Try, containing either the claims set or a failure indicating the reason authentication failed. This is
   *         to make composition easier.
   */
  def checkExpiry(claims:JWTClaimsSet):Either[LoginResult,LoginResultOK[JWTClaimsSet]] = {
    if(claims.getExpirationTime.before(Date.from(Instant.now()))) {
      logger.debug(s"JWT was valid but expired at ${claims.getExpirationTime.formatted("YYYY-MM-dd HH:mm:ss")}")
      Left(LoginResultExpired(claims.getSubject))
    } else {
      Right(LoginResultOK(claims))
    }
  }

  /**
    * performs the JWT authentication against a given header.
   * This should not be called directly, but is done in the Security trait as part of IsAuthenticated or IsAdmin.
    * @param rh request header
    * @return a LoginResult subclass, as a Left if something failed or a Right if it succeeded
    */
  def apply(rh: RequestHeader): Either[LoginResult,LoginResultOK[JWTClaimsSet]] = {
    rh.headers.get("Authorization") match {
      case Some(authValue)=>
        extractAuthorization(authValue)
          .flatMap(validateToken)
          .flatMap(result=>checkExpiry(result.content))
          .map(result=>{
            rh.addAttr(BearerTokenAuth.ClaimsAttributeKey, result.content)
            result
          })
      case None=>
        logger.error("Attempt to access without authorization")
        Left(LoginResultNotPresent)
    }
  }
}