[#SSL_CTX_set_alpn_select_cb]
= SSL_CTX_set_alpn_select_cb
:mrdocs:

Register the server callback that selects an ALPN protocol during the handshake.

== Synopsis

Declared in `<openssl/ssl.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
SSL_CTX_set_alpn_select_cb(
    xref:SSL_CTX.adoc[SSL_CTX]* ctx,
    xref:SSL_CTX_alpn_select_cb_func.adoc[SSL_CTX_alpn_select_cb_func] cb,
    void* arg);
----

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| SSL context whose ALPN select callback is set.
| *cb*
| Callback invoked with the client's offered protocols, or NULL to clear.
| *arg*
| User pointer passed through to `cb` as its final argument.
|===


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