Generic credential auth endpoint for call links

service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerConfiguration.java

@@ -20,6 +20,7 @@ import org.whispersystems.textsecuregcm.configuration.ArtServiceConfiguration;
 import org.whispersystems.textsecuregcm.configuration.AwsAttachmentsConfiguration;
 import org.whispersystems.textsecuregcm.configuration.BadgesConfiguration;
 import org.whispersystems.textsecuregcm.configuration.BraintreeConfiguration;
+import org.whispersystems.textsecuregcm.configuration.CallLinkConfiguration;
 import org.whispersystems.textsecuregcm.configuration.CdnConfiguration;
 import org.whispersystems.textsecuregcm.configuration.DatadogConfiguration;
 import org.whispersystems.textsecuregcm.configuration.DirectoryConfiguration;
@@ -219,6 +220,11 @@ public class WhisperServerConfiguration extends Configuration {
   @JsonProperty
   private ArtServiceConfiguration artService;
 
+  @Valid
+  @NotNull
+  @JsonProperty
+  private CallLinkConfiguration callLink;
+
   @Valid
   @NotNull
   @JsonProperty
@@ -371,6 +377,10 @@ public class WhisperServerConfiguration extends Configuration {
     return datadog;
   }
 
+  public CallLinkConfiguration getCallLinkConfiguration() {
+    return callLink;
+  }
+
   public UnidentifiedDeliveryConfiguration getDeliveryCertificate() {
     return unidentifiedDelivery;
   }

service/src/main/java/org/whispersystems/textsecuregcm/WhisperServerService.java

@@ -89,6 +89,7 @@ import org.whispersystems.textsecuregcm.controllers.AccountControllerV2;
 import org.whispersystems.textsecuregcm.controllers.ArtController;
 import org.whispersystems.textsecuregcm.controllers.AttachmentControllerV2;
 import org.whispersystems.textsecuregcm.controllers.AttachmentControllerV3;
+import org.whispersystems.textsecuregcm.controllers.CallLinkController;
 import org.whispersystems.textsecuregcm.controllers.CertificateController;
 import org.whispersystems.textsecuregcm.controllers.ChallengeController;
 import org.whispersystems.textsecuregcm.controllers.DeviceController;
@@ -490,6 +491,9 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
         config.getArtServiceConfiguration());
     ExternalServiceCredentialsGenerator svr2CredentialsGenerator = SecureValueRecovery2Controller.credentialsGenerator(
         config.getSvr2Configuration());
+    ExternalServiceCredentialsGenerator callLinkCredentialsGenerator = CallLinkController.credentialsGenerator(
+        config.getCallLinkConfiguration()
+    );
 
     dynamicConfigurationManager.start();
 
@@ -774,6 +778,7 @@ public class WhisperServerService extends Application<WhisperServerConfiguration
         new ArtController(rateLimiters, artCredentialsGenerator),
         new AttachmentControllerV2(rateLimiters, config.getAwsAttachmentsConfiguration().getAccessKey(), config.getAwsAttachmentsConfiguration().getAccessSecret(), config.getAwsAttachmentsConfiguration().getRegion(), config.getAwsAttachmentsConfiguration().getBucket()),
         new AttachmentControllerV3(rateLimiters, config.getGcpAttachmentsConfiguration().getDomain(), config.getGcpAttachmentsConfiguration().getEmail(), config.getGcpAttachmentsConfiguration().getMaxSizeInBytes(), config.getGcpAttachmentsConfiguration().getPathPrefix(), config.getGcpAttachmentsConfiguration().getRsaSigningKey()),
+        new CallLinkController(callLinkCredentialsGenerator),
         new CertificateController(new CertificateGenerator(config.getDeliveryCertificate().getCertificate(), config.getDeliveryCertificate().getPrivateKey(), config.getDeliveryCertificate().getExpiresDays()), zkAuthOperations, clock),
         new ChallengeController(rateLimitChallengeManager),
         new DeviceController(pendingDevicesManager, accountsManager, messagesManager, keys, rateLimiters, config.getMaxDevices()),

service/src/main/java/org/whispersystems/textsecuregcm/auth/ExternalServiceCredentialsGenerator.java

@@ -11,8 +11,10 @@ import static org.whispersystems.textsecuregcm.util.HmacUtils.hmac256TruncatedTo
 import static org.whispersystems.textsecuregcm.util.HmacUtils.hmacHexStringsEqual;
 
 import java.time.Clock;
+import java.time.Instant;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.function.Function;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.commons.lang3.Validate;
 
@@ -28,6 +30,10 @@ public class ExternalServiceCredentialsGenerator {
 
   private final boolean truncateSignature;
 
+  private final String usernameTimestampPrefix;
+
+  private final Function<Instant, Instant> usernameTimestampTruncator;
+
   private final Clock clock;
 
   private final int truncateLength;
@@ -41,14 +47,22 @@ public class ExternalServiceCredentialsGenerator {
       final byte[] userDerivationKey,
       final boolean prependUsername,
       final boolean truncateSignature,
-      final Clock clock,
-      final int truncateLength) {
+      final int truncateLength,
+      final String usernameTimestampPrefix,
+      final Function<Instant, Instant> usernameTimestampTruncator,
+      final Clock clock) {
     this.key = requireNonNull(key);
     this.userDerivationKey = requireNonNull(userDerivationKey);
     this.prependUsername = prependUsername;
     this.truncateSignature = truncateSignature;
+    this.usernameTimestampPrefix = usernameTimestampPrefix;
+    this.usernameTimestampTruncator = usernameTimestampTruncator;
     this.clock = requireNonNull(clock);
     this.truncateLength = truncateLength;
+
+    if (hasUsernameTimestampPrefix() ^ hasUsernameTimestampTruncator()) {
+      throw new RuntimeException("Configured to have only one of (usernameTimestampPrefix, usernameTimestampTruncator)");
+    }
   }
 
   /**
@@ -66,13 +80,34 @@ public class ExternalServiceCredentialsGenerator {
    * @return an instance of {@link ExternalServiceCredentials}
    */
   public ExternalServiceCredentials generateFor(final String identity) {
+    if (usernameIsTimestamp()) {
+      throw new RuntimeException("Configured to use timestamp as username");
+    }
+
+    return generate(identity);
+  }
+
+  /**
+   * Generates `ExternalServiceCredentials` using a prefix concatenated with a truncated timestamp as the username, following this generator's configuration.
+   * @return an instance of {@link ExternalServiceCredentials}
+   */
+  public ExternalServiceCredentials generateWithTimestampAsUsername() {
+    if (!usernameIsTimestamp()) {
+      throw new RuntimeException("Not configured to use timestamp as username");
+    }
+
+    final String truncatedTimestampSeconds = String.valueOf(usernameTimestampTruncator.apply(clock.instant()).getEpochSecond());
+    return generate(usernameTimestampPrefix + DELIMITER + truncatedTimestampSeconds);
+  }
+
+  private ExternalServiceCredentials generate(final String identity) {
     final String username = shouldDeriveUsername()
         ? hmac256TruncatedToHexString(userDerivationKey, identity, truncateLength)
         : identity;
 
     final long currentTimeSeconds = currentTimeSeconds();
 
-    final String dataToSign = username + DELIMITER + currentTimeSeconds;
+    final String dataToSign = usernameIsTimestamp() ? username : username + DELIMITER + currentTimeSeconds;
 
     final String signature = truncateSignature
         ? hmac256TruncatedToHexString(key, dataToSign, truncateLength)
@@ -84,7 +119,7 @@ public class ExternalServiceCredentialsGenerator {
   }
 
   /**
-   * In certain cases, identity (as it was passed to `generateFor` method)
+   * In certain cases, identity (as it was passed to `generate` method)
    * is a part of the signature (`password`, in terms of `ExternalServiceCredentials`) string itself.
    * For such cases, this method returns the value of the identity string.
    * @param password `password` part of `ExternalServiceCredentials`
@@ -96,9 +131,15 @@ public class ExternalServiceCredentialsGenerator {
       return Optional.empty();
     }
     // checking for the case of unexpected format
-    return StringUtils.countMatches(password, DELIMITER) == 2
-        ? Optional.of(password.substring(0, password.indexOf(DELIMITER)))
-        : Optional.empty();
+    if (StringUtils.countMatches(password, DELIMITER) == 2) {
+      if (usernameIsTimestamp()) {
+        final int indexOfSecondDelimiter = password.indexOf(DELIMITER, password.indexOf(DELIMITER) + 1);
+        return Optional.of(password.substring(0, indexOfSecondDelimiter));
+      } else {
+        return Optional.of(password.substring(0, password.indexOf(DELIMITER)));
+      }
+    }
+    return Optional.empty();
   }
 
   /**
@@ -115,7 +156,7 @@ public class ExternalServiceCredentialsGenerator {
 
     // making sure password format matches our expectations based on the generator configuration
     if (parts.length == 3 && prependUsername) {
-      final String username = parts[0];
+      final String username = usernameIsTimestamp() ? parts[0] + DELIMITER + parts[1] : parts[0];
       // username has to match the one from `credentials`
       if (!credentials.username().equals(username)) {
         return Optional.empty();
@@ -130,7 +171,7 @@ public class ExternalServiceCredentialsGenerator {
       return Optional.empty();
     }
 
-    final String signedData = credentials.username() + DELIMITER + timestampSeconds;
+    final String signedData = usernameIsTimestamp() ? credentials.username() : credentials.username() + DELIMITER + timestampSeconds;
     final String expectedSignature = truncateSignature
         ? hmac256TruncatedToHexString(key, signedData, truncateLength)
         : hmac256ToHexString(key, signedData);
@@ -158,6 +199,18 @@ public class ExternalServiceCredentialsGenerator {
     return userDerivationKey.length > 0;
   }
 
+  private boolean hasUsernameTimestampPrefix() {
+    return usernameTimestampPrefix != null;
+  }
+
+  private boolean hasUsernameTimestampTruncator() {
+    return usernameTimestampTruncator != null;
+  }
+
+  private boolean usernameIsTimestamp() {
+    return hasUsernameTimestampPrefix() && hasUsernameTimestampTruncator();
+  }
+
   private long currentTimeSeconds() {
     return clock.instant().getEpochSecond();
   }
@@ -174,6 +227,10 @@ public class ExternalServiceCredentialsGenerator {
 
     private int truncateLength = 10;
 
+    private String usernameTimestampPrefix = null;
+
+    private Function<Instant, Instant> usernameTimestampTruncator = null;
+
     private Clock clock = Clock.systemUTC();
 
 
@@ -208,9 +265,15 @@ public class ExternalServiceCredentialsGenerator {
       return this;
     }
 
+    public Builder withUsernameTimestampTruncatorAndPrefix(final Function<Instant, Instant> truncator, final String prefix) {
+      this.usernameTimestampTruncator = truncator;
+      this.usernameTimestampPrefix = prefix;
+      return this;
+    }
+
     public ExternalServiceCredentialsGenerator build() {
       return new ExternalServiceCredentialsGenerator(
-          key, userDerivationKey, prependUsername, truncateSignature, clock, truncateLength);
+          key, userDerivationKey, prependUsername, truncateSignature, truncateLength, usernameTimestampPrefix, usernameTimestampTruncator, clock);
     }
   }
 }

service/src/main/java/org/whispersystems/textsecuregcm/configuration/CallLinkConfiguration.java

@@ -0,0 +1,9 @@
+package org.whispersystems.textsecuregcm.configuration;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import org.whispersystems.textsecuregcm.util.ExactlySize;
+import javax.validation.constraints.NotEmpty;
+import java.util.HexFormat;
+
+public record CallLinkConfiguration (@ExactlySize({32}) byte[] userAuthenticationTokenSharedSecret) {
+}

service/src/main/java/org/whispersystems/textsecuregcm/controllers/CallLinkController.java

@@ -0,0 +1,56 @@
+package org.whispersystems.textsecuregcm.controllers;
+
+import com.codahale.metrics.annotation.Timed;
+import com.google.common.annotations.VisibleForTesting;
+import io.dropwizard.auth.Auth;
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import org.whispersystems.textsecuregcm.auth.AuthenticatedAccount;
+import org.whispersystems.textsecuregcm.auth.ExternalServiceCredentials;
+import org.whispersystems.textsecuregcm.auth.ExternalServiceCredentialsGenerator;
+import org.whispersystems.textsecuregcm.configuration.CallLinkConfiguration;
+import javax.ws.rs.GET;
+import javax.ws.rs.Path;
+import javax.ws.rs.Produces;
+import javax.ws.rs.core.MediaType;
+import java.time.Clock;
+import java.time.temporal.ChronoUnit;
+import java.util.Optional;
+
+@Path("/v1/call-link")
+@io.swagger.v3.oas.annotations.tags.Tag(name = "CallLink")
+public class CallLinkController {
+  @VisibleForTesting
+  public static final String ANONYMOUS_CREDENTIAL_PREFIX = "anon";
+
+  private final ExternalServiceCredentialsGenerator callingFrontendServiceCredentialGenerator;
+
+  public CallLinkController(
+      ExternalServiceCredentialsGenerator callingFrontendServiceCredentialGenerator
+  ) {
+    this.callingFrontendServiceCredentialGenerator = callingFrontendServiceCredentialGenerator;
+  }
+
+  public static ExternalServiceCredentialsGenerator credentialsGenerator(final CallLinkConfiguration cfg) {
+    return ExternalServiceCredentialsGenerator
+        .builder(cfg.userAuthenticationTokenSharedSecret())
+        .withUsernameTimestampTruncatorAndPrefix(timestamp -> timestamp.truncatedTo(ChronoUnit.DAYS), ANONYMOUS_CREDENTIAL_PREFIX)
+        .build();
+  }
+  @Timed
+  @GET
+  @Path("/auth")
+  @Produces(MediaType.APPLICATION_JSON)
+  @Operation(
+      summary = "Generate credentials for calling frontend",
+      description = """
+          These credentials enable clients to prove to calling frontend that they were a Signal user within the last day.
+          For client privacy, timestamps are truncated to 1 day granularity and the token does not include or derive from an ACI.
+          """
+  )
+  @ApiResponse(responseCode = "200", description = "`JSON` with generated credentials.", useReturnTypeSchema = true)
+  @ApiResponse(responseCode = "401", description = "Account authentication check failed.")
+  public ExternalServiceCredentials getAuth(@Auth AuthenticatedAccount auth) {
+    return callingFrontendServiceCredentialGenerator.generateWithTimestampAsUsername();
+  }
+}