hmac-sha2-256
hmac-sha2-512
hmac-sha1
hmac-sha1-96
```

### Certificate-based authentication

`--sftp=trusted-user-ca-key=...` specifies a file containing public key of certificate authority that is trusted
to sign user certificates for authentication.

Implementation is identical with "TrustedUserCAKeys" setting in OpenSSH server with exception that only one CA
key can be defined.

   will call `SecretManager.GenerateSecret(resourceName)`
1. When `GenerateSecret` is called, the `SecretManager` is expected to return a new certificate. This can occur in a few ways.
   1. The most common method (pictured above) is to sign a new certificate by calling the configured CA. Typically, this is Istiod.
   1. If the certificate is not yet expired, the `SecretManager` also can return a cache response. In practice, this would

              <version>3.0.1</version>
              <executions>
                <execution>
                  <id>sign-artifacts</id>
                  <phase>verify</phase>
                  <goals>
                    <goal>sign</goal>
                  </goals>
                </execution>
              </executions>
            </plugin>
          </plugins>
      </build>

              <version>3.0.1</version>
              <executions>
                <execution>
                  <id>sign-artifacts</id>
                  <phase>verify</phase>
                  <goals>
                    <goal>sign</goal>
                  </goals>
                </execution>
              </executions>
            </plugin>
          </plugins>
      </build>

        request.flags2 |= flags2;
        request.useUnicode = useUnicode;
        request.response = response; /* needed by sign */
        if (request.digest == null)
            request.digest = digest; /* for sign called in encode */

        try {
            if (response == null) {
                doSend0( request );
                return;

        this.signKey = deriveKey(mk, C2S_SIGN_CONSTANT);
        this.verifyKey = deriveKey(mk, S2C_SIGN_CONSTANT);

        if ( log.isDebugEnabled() ) {
            log.debug("Sign key is " + Hexdump.toHexString(this.signKey));
            log.debug("Verify key is " + Hexdump.toHexString(this.verifyKey));
        }

        this.sealClientKey = deriveKey(mk, C2S_SEAL_CONSTANT);

   *       the same.
   *   <li>The special characters ".", "-", "*", and "_" remain the same.
   *   <li>The space character " " is converted into a plus sign "+".
   *   <li>All other characters are converted into one or more bytes using UTF-8 encoding and each
   *       byte is then represented by the 3-character string "%XY", where "XY" is the two-digit,

to generate a trusted root certificate, an intermediate certificate, and a server certificate.
We use `certificateAuthority(int)` to create certificates that can sign other certificates. The
int specifies how many intermediate certificates are allowed beneath it in the chain.

```java
HeldCertificate rootCertificate = new HeldCertificate.Builder()
    .certificateAuthority(1)

      return Byte.MAX_VALUE;
    }
    if (value < Byte.MIN_VALUE) {
      return Byte.MIN_VALUE;
    }
    return (byte) value;
  }

  /**
   * Compares the two specified {@code byte} values. The sign of the value returned is the same as
   * that of {@code ((Byte) a).compareTo(b)}.
   *
   * <p><b>Note:</b> this method behaves identically to {@link Byte#compare}.
   *
   * @param a the first {@code byte} to compare

   *       the same.
   *   <li>The special characters ".", "-", "*", and "_" remain the same.
   *   <li>The space character " " is converted into a plus sign "+".
   *   <li>All other characters are converted into one or more bytes using UTF-8 encoding and each
   *       byte is then represented by the 3-character string "%XY", where "XY" is the two-digit,