public TlsProviderBuilder keyPair(String hostname, TlsKeyPair tlsKeyPair) {
        requireNonNull(hostname, "hostname");
        requireNonNull(tlsKeyPair, "tlsKeyPair");
        tlsKeyPairsBuilder.put(normalize(hostname), tlsKeyPair);
        return this;
    }
Sets the {@link TlsKeyPair} for the specified (optionally wildcard) {@code hostname}.

<p><a href="https://en.wikipedia.org/wiki/Wildcard_DNS_record">DNS wildcard</a> is supported as hostname.
The wildcard will only match one sub-domain deep and only when wildcard is used as the most-left label.
For example, *.armeria.dev will match foo.armeria.dev but NOT bar.foo.armeria.dev

<p>Note that {@code "*"} is a special hostname which matches any hostname which may be used to find the
{@link TlsKeyPair} for the {@linkplain ServerBuilder#defaultVirtualHost() default virtual host}.

<p>The {@link TlsKeyPair} will be used for
<a href="https://www.cloudflare.com/learning/access-management/what-is-mutual-tls/">client certificate authentication</a>
when it is used for a client.
core/src/main/java/com/linecorp/armeria/common/TlsProviderBuilder.java