[#SSL_CTX_add_custom_ext]
= SSL_CTX_add_custom_ext
:mrdocs:

Register a custom TLS extension for client and/or server using the extended callback API.

== Synopsis

Declared in `<openssl/ssl.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
SSL_CTX_add_custom_ext(
    xref:SSL_CTX.adoc[SSL_CTX]* ctx,
    unsigned int ext_type,
    unsigned int context,
    xref:SSL_custom_ext_add_cb_ex.adoc[SSL_custom_ext_add_cb_ex] add_cb,
    xref:SSL_custom_ext_free_cb_ex.adoc[SSL_custom_ext_free_cb_ex] free_cb,
    void* add_arg,
    xref:SSL_custom_ext_parse_cb_ex.adoc[SSL_custom_ext_parse_cb_ex] parse_cb,
    void* parse_arg);
----

== Return Value

1 on success, or 0 on error.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *ctx*
| SSL context that sends or receives the extension.
| *ext_type*
| Extension type code (must not collide with OpenSSL‐built‐in handlers).
| *context*
| Bitmask of SSL_EXT_* contexts in which the extension is relevant.
| *add_cb*
| Callback that constructs extension data to send, or NULL.
| *free_cb*
| Optional callback to free data produced by `add_cb.`
| *add_arg*
| Application argument passed to `add_cb` and `free_cb.`
| *parse_cb*
| Callback that parses extension data received from the peer, or NULL.
| *parse_arg*
| Application argument passed to `parse_cb.`
|===


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