![[APACHE DOCUMENTATION]](../images/sub.gif)
Apache HTTP Server Version 2.0
Apache Module mod_ssl
|
Summary
This module provides SSL v2/v3 and TLS v1 support for the Apache HTTP Server. It was contributed by Ralf S. Engeschall based on his mod_ssl project and originally derived from work by Ben Laurie.
This module relies on OpenSSL to provide the cryptography engine.
Further details, discussion, and examples are provided in the SSL documentation.
Directives
- SSLCACertificateFile
- SSLCACertificatePath
- SSLCARevocationFile
- SSLCARevocationPath
- SSLCertificateChainFile
- SSLCertificateFile
- SSLCertificateKeyFile
- SSLCipherSuite
- SSLEngine
- SSLMutex
- SSLOptions
- SSLPassPhraseDialog
- SSLProtocol
- SSLRandomSeed
- SSLRequire
- SSLRequireSSL
- SSLSessionCache
- SSLSessionCacheTimeout
- SSLVerifyClient
- SSLVerifyDepth
Environment Variables
This module provides a lot of SSL information as additional environment variables to the SSI and CGI namespace. The generated variables are listed in the table below. For backward compatibility the information can be made available under different names, too. Look in the Compatibility chapter for details on the compatibility variables.
|
Custom Log Formats
When mod_ssl is built into Apache or at least
loaded (under DSO situation) additional functions exist for the Custom Log Format of
mod_log_config. First there is an
additional ``%{varname}x''
eXtension format function which can be used to expand any variables
provided by any module, especially those provided by mod_ssl which can
you find in the above table.
For backward compatibility there is additionally a special
``%{name}c'' cryptography format function
provided. Information about this function is provided in the Compatibility chapter.
Example:
CustomLog logs/ssl_request_log \ "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
SSLCACertificateFile Directive
|
This directive sets the all-in-one file where you can assemble the
Certificates of Certification Authorities (CA) whose clients you deal
with. These are used for Client Authentication. Such a file is simply the
concatenation of the various PEM-encoded Certificate files, in order of
preference. This can be used alternatively and/or additionally to
SSLCACertificatePath.
Example
SSLCACertificateFile /usr/local/apache/conf/ssl.crt/ca-bundle-client.crt
SSLCACertificatePath Directive
|
This directive sets the directory where you keep the Certificates of Certification Authorities (CAs) whose clients you deal with. These are used to verify the client certificate on Client Authentication.
The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you can't just place the Certificate files
there: you also have to create symbolic links named
hash-value.N. And you should always make sure this directory
contains the appropriate symbolic links. Use the Makefile which
comes with mod_ssl to accomplish this task.
Example
SSLCACertificatePath /usr/local/apache/conf/ssl.crt/
SSLCARevocationFile Directive
|
This directive sets the all-in-one file where you can
assemble the Certificate Revocation Lists (CRL) of Certification
Authorities (CA) whose clients you deal with. These are used
for Client Authentication. Such a file is simply the concatenation of
the various PEM-encoded CRL files, in order of preference. This can be
used alternatively and/or additionally to SSLCARevocationPath.
Example
SSLCARevocationFile /usr/local/apache/conf/ssl.crl/ca-bundle-client.crl
SSLCARevocationPath Directive
|
This directive sets the directory where you keep the Certificate Revocation Lists (CRL) of Certification Authorities (CAs) whose clients you deal with. These are used to revoke the client certificate on Client Authentication.
The files in this directory have to be PEM-encoded and are accessed through
hash filenames. So usually you have not only to place the CRL files there.
Additionally you have to create symbolic links named
hash-value.rN. And you should always make sure this directory
contains the appropriate symbolic links. Use the Makefile which
comes with mod_ssl to accomplish this task.
Example
SSLCARevocationPath /usr/local/apache/conf/ssl.crl/
SSLCertificateChainFile Directive
|
This directive sets the optional all-in-one file where you can assemble the certificates of Certification Authorities (CA) which form the certificate chain of the server certificate. This starts with the issuing CA certificate of of the server certificate and can range up to the root CA certificate. Such a file is simply the concatenation of the various PEM-encoded CA Certificate files, usually in certificate chain order.
This should be used alternatively and/or additionally to SSLCACertificatePath for explicitly
constructing the server certificate chain which is sent to the browser
in addition to the server certificate. It is especially useful to
avoid conflicts with CA certificates when using client
authentication. Because although placing a CA certificate of the
server certificate chain into SSLCACertificatePath has the same effect
for the certificate chain construction, it has the side-effect that
client certificates issued by this same CA certificate are also
accepted on client authentication. That's usually not one expect.
But be careful: Providing the certificate chain works only if you are using a single (either RSA or DSA) based server certificate. If you are using a coupled RSA+DSA certificate pair, this will work only if actually both certificates use the same certificate chain. Else the browsers will be confused in this situation.
Example
SSLCertificateChainFile /usr/local/apache/conf/ssl.crt/ca.crt
SSLCertificateFile Directive
|
This directive points to the PEM-encoded Certificate file for the server and optionally also to the corresponding RSA or DSA Private Key file for it (contained in the same file). If the contained Private Key is encrypted the Pass Phrase dialog is forced at startup time. This directive can be used up to two times (referencing different filenames) when both a RSA and a DSA based server certificate is used in parallel.
Example
SSLCertificateFile /usr/local/apache/conf/ssl.crt/server.crt
SSLCertificateKeyFile Directive
|
This directive points to the PEM-encoded Private Key file for the
server. If the Private Key is not combined with the Certificate in the
SSLCertificateFile, use this additional directive to
point to the file with the stand-alone Private Key. When
SSLCertificateFile is used and the file
contains both the Certificate and the Private Key this directive need
not be used. But we strongly discourage this practice. Instead we
recommend you to separate the Certificate and the Private Key. If the
contained Private Key is encrypted, the Pass Phrase dialog is forced
at startup time. This directive can be used up to two times
(referencing different filenames) when both a RSA and a DSA based
private key is used in parallel.
Example
SSLCertificateKeyFile /usr/local/apache/conf/ssl.key/server.key
SSLCipherSuite Directive
|
This complex directive uses a colon-separated cipher-spec string consisting of OpenSSL cipher specifications to configure the Cipher Suite the client is permitted to negotiate in the SSL handshake phase. Notice that this directive can be used both in per-server and per-directory context. In per-server context it applies to the standard SSL handshake when a connection is established. In per-directory context it forces a SSL renegotation with the reconfigured Cipher Suite after the HTTP request was read but before the HTTP response is sent.
An SSL cipher specification in cipher-spec is composed of 4 major attributes plus a few extra minor ones:
- Key Exchange Algorithm:
RSA or Diffie-Hellman variants. - Authentication Algorithm:
RSA, Diffie-Hellman, DSS or none. - Cipher/Encryption Algorithm:
DES, Triple-DES, RC4, RC2, IDEA or none. - MAC Digest Algorithm:
MD5, SHA or SHA1.
An SSL cipher can also be an export cipher and is either a SSLv2 or SSLv3/TLSv1 cipher (here TLSv1 is equivalent to SSLv3). To specify which ciphers to use, one can either specify all the Ciphers, one at a time, or use aliases to specify the preference and order for the ciphers (see Table 1).
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Now where this becomes interesting is that these can be put together
to specify the order and ciphers you wish to use. To speed this up
there are also aliases (SSLv2, SSLv3, TLSv1, EXP, LOW, MEDIUM,
HIGH) for certain groups of ciphers. These tags can be joined
together with prefixes to form the cipher-spec. Available
prefixes are:
- none: add cipher to list
+: add ciphers to list and pull them to current location in list-: remove cipher from list (can be added later again)!: kill cipher from list completely (can not be added later again)
A simpler way to look at all of this is to use the ``openssl ciphers
-v'' command which provides a nice way to successively create the
correct cipher-spec string. The default cipher-spec string
is ``ALL:!ADH:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP'' which
means the following: first, remove from consideration any ciphers that do not
authenticate, i.e. for SSL only the Anonymous Diffie-Hellman ciphers. Next,
use ciphers using RC4 and RSA. Next include the high, medium and then the low
security ciphers. Finally pull all SSLv2 and export ciphers to the
end of the list.
The complete list of particular RSA & DH ciphers for SSL is given in Table 2.
Example
SSLCipherSuite RSA:!EXP:!NULL:+HIGH:+MEDIUM:-LOW
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SSLEngine Directive
|
This directive toggles the usage of the SSL/TLS Protocol Engine. This
is usually used inside a <VirtualHost> section to enable SSL/TLS for a
particular virtual host. By default the SSL/TLS Protocol Engine is
disabled for both the main server and all configured virtual hosts.
Example
<VirtualHost _default_:443>
SSLEngine on
...
</VirtualHost>
SSLMutex Directive
|
This configures the SSL engine's semaphore (aka. lock) which is used for mutual exclusion of operations which have to be done in a synchronized way between the pre-forked Apache server processes. This directive can only be used in the global server context because it's only useful to have one global mutex.
The following Mutex types are available:
noneThis is the default where no Mutex is used at all. Use it at your own risk. But because currently the Mutex is mainly used for synchronizing write access to the SSL Session Cache you can live without it as long as you accept a sometimes garbled Session Cache. So it's not recommended to leave this the default. Instead configure a real Mutex.
file:/path/to/mutexThis is the portable and (under Unix) always provided Mutex variant where a physical (lock-)file is used as the Mutex. Always use a local disk filesystem for
/path/to/mutexand never a file residing on a NFS- or AFS-filesystem. Note: Internally, the Process ID (PID) of the Apache parent process is automatically appended to/path/to/mutexto make it unique, so you don't have to worry about conflicts yourself. Notice that this type of mutex is not available under the Win32 environment. There you have to use the semaphore mutex.semThis is the most elegant but also most non-portable Mutex variant where a SysV IPC Semaphore (under Unix) and a Windows Mutex (under Win32) is used when possible. It is only available when the underlying platform supports it.
Example
SSLMutex file:/usr/local/apache/logs/ssl_mutex
SSLOptions Directive
|
This directive can be used to control various run-time options on a
per-directory basis. Normally, if multiple SSLOptions
could apply to a directory, then the most specific one is taken
completely; the options are not merged. However if all the
options on the SSLOptions directive are preceded by a
plus (+) or minus (-) symbol, the options
are merged. Any options preceded by a + are added to the
options currently in force, and any options preceded by a
- are removed from the options currently in force.
The available options are:
StdEnvVarsWhen this option is enabled, the standard set of SSL related CGI/SSI environment variables are created. This per default is disabled for performance reasons, because the information extraction step is a rather expensive operation. So one usually enables this option for CGI and SSI requests only.
CompatEnvVarsWhen this option is enabled, additional CGI/SSI environment variables are created for backward compatibility to other Apache SSL solutions. Look in the Compatibility chapter for details on the particular variables generated.
ExportCertDataWhen this option is enabled, additional CGI/SSI environment variables are created:
SSL_SERVER_CERT,SSL_CLIENT_CERTandSSL_CLIENT_CERT_CHAINn (with n = 0,1,2,..). These contain the PEM-encoded X.509 Certificates of server and client for the current HTTPS connection and can be used by CGI scripts for deeper Certificate checking. Additionally all other certificates of the client certificate chain are provided, too. This bloats up the environment a little bit which is why you have to use this option to enable it on demand.FakeBasicAuthWhen this option is enabled, the Subject Distinguished Name (DN) of the Client X509 Certificate is translated into a HTTP Basic Authorization username. This means that the standard Apache authentication methods can be used for access control. The user name is just the Subject of the Client's X509 Certificate (can be determined by running OpenSSL's
openssl x509command:openssl x509 -noout -subject -incertificate.crt). Note that no password is obtained from the user. Every entry in the user file needs this password: ``xxj31ZMTZzkVA'', which is the DES-encrypted version of the word `password''. Those who live under MD5-based encryption (for instance under FreeBSD or BSD/OS, etc.) should use the following MD5 hash of the same word: ``$1$OXLyS...$Owx8s2/m9/gfkcRVXzgoE/''.StrictRequireThis forces forbidden access when
SSLRequireSSLorSSLRequiresuccessfully decided that access should be forbidden. Usually the default is that in the case where a ``Satisfy any'' directive is used, and other access restrictions are passed, denial of access due toSSLRequireSSLorSSLRequireis overridden (because that's how the ApacheSatisfymechanism should work.) But for strict access restriction you can useSSLRequireSSLand/orSSLRequirein combination with an ``SSLOptions +StrictRequire''. Then an additional ``Satisfy Any'' has no chance once mod_ssl has decided to deny access.OptRenegotiateThis enables optimized SSL connection renegotiation handling when SSL directives are used in per-directory context. By default a strict scheme is enabled where every per-directory reconfiguration of SSL parameters causes a full SSL renegotiation handshake. When this option is used mod_ssl tries to avoid unnecessary handshakes by doing more granular (but still safe) parameter checks. Nevertheless these granular checks sometimes maybe not what the user expects, so enable this on a per-directory basis only, please.
Example
SSLOptions +FakeBasicAuth -StrictRequire
<Files ~ "\.(cgi|shtml)$">
SSLOptions +StdEnvVars +CompatEnvVars -ExportCertData
<Files>
SSLPassPhraseDialog Directive
|
When Apache starts up it has to read the various Certificate (see
SSLCertificateFile) and
Private Key (see SSLCertificateKeyFile) files of the
SSL-enabled virtual servers. Because for security reasons the Private
Key files are usually encrypted, mod_ssl needs to query the
administrator for a Pass Phrase in order to decrypt those files. This
query can be done in two ways which can be configured by
type:
builtinThis is the default where an interactive terminal dialog occurs at startup time just before Apache detaches from the terminal. Here the administrator has to manually enter the Pass Phrase for each encrypted Private Key file. Because a lot of SSL-enabled virtual hosts can be configured, the following reuse-scheme is used to minimize the dialog: When a Private Key file is encrypted, all known Pass Phrases (at the beginning there are none, of course) are tried. If one of those known Pass Phrases succeeds no dialog pops up for this particular Private Key file. If none succeeded, another Pass Phrase is queried on the terminal and remembered for the next round (where it perhaps can be reused).
This scheme allows mod_ssl to be maximally flexible (because for N encrypted Private Key files you can use N different Pass Phrases - but then you have to enter all of them, of course) while minimizing the terminal dialog (i.e. when you use a single Pass Phrase for all N Private Key files this Pass Phrase is queried only once).
exec:/path/to/programHere an external program is configured which is called at startup for each encrypted Private Key file. It is called with two arguments (the first is of the form ``
servername:portnumber'', the second is either ``RSA'' or ``DSA''), which indicate for which server and algorithm it has to print the corresponding Pass Phrase tostdout. The intent is that this external program first runs security checks to make sure that the system is not compromised by an attacker, and only when these checks were passed successfully it provides the Pass Phrase.Both these security checks, and the way the Pass Phrase is determined, can be as complex as you like. Mod_ssl just defines the interface: an executable program which provides the Pass Phrase on
stdout. Nothing more or less! So, if you're really paranoid about security, here is your interface. Anything else has to be left as an exercise to the administrator, because local security requirements are so different.The reuse-algorithm above is used here, too. In other words: The external program is called only once per unique Pass Phrase.
Example:
SSLPassPhraseDialog exec:/usr/local/apache/sbin/pp-filter
SSLProtocol Directive
|
This directive can be used to control the SSL protocol flavors mod_ssl should use when establishing its server environment. Clients then can only connect with one of the provided protocols.
The available (case-insensitive) protocols are:
SSLv2This is the Secure Sockets Layer (SSL) protocol, version 2.0. It is the original SSL protocol as designed by Netscape Corporation.
SSLv3This is the Secure Sockets Layer (SSL) protocol, version 3.0. It is the successor to SSLv2 and the currently (as of February 1999) de-facto standardized SSL protocol from Netscape Corporation. It's supported by almost all popular browsers.
TLSv1This is the Transport Layer Security (TLS) protocol, version 1.0. It is the successor to SSLv3 and currently (as of February 1999) still under construction by the Internet Engineering Task Force (IETF). It's still not supported by any popular browsers.
AllThis is a shortcut for ``
+SSLv2 +SSLv3 +TLSv1'' and a convinient way for enabling all protocols except one when used in combination with the minus sign on a protocol as the example above shows.
Example
# enable SSLv3 and TLSv1, but not SSLv2
SSLProtocol all -SSLv2
SSLRandomSeed Directive
|
This configures one or more sources for seeding the Pseudo Random Number
Generator (PRNG) in OpenSSL at startup time (context is
startup) and/or just before a new SSL connection is established
(context is connect). This directive can only be used
in the global server context because the PRNG is a global facility.
The following source variants are available:
builtinThis is the always available builtin seeding source. It's usage consumes minimum CPU cycles under runtime and hence can be always used without drawbacks. The source used for seeding the PRNG contains of the current time, the current process id and (when applicable) a randomly choosen 1KB extract of the inter-process scoreboard structure of Apache. The drawback is that this is not really a strong source and at startup time (where the scoreboard is still not available) this source just produces a few bytes of entropy. So you should always, at least for the startup, use an additional seeding source.
file:/path/to/sourceThis variant uses an external file
/path/to/sourceas the source for seeding the PRNG. When bytes is specified, only the first bytes number of bytes of the file form the entropy (and bytes is given to/path/to/sourceas the first argument). When bytes is not specified the whole file forms the entropy (and0is given to/path/to/sourceas the first argument). Use this especially at startup time, for instance with an available/dev/randomand/or/dev/urandomdevices (which usually exist on modern Unix derivates like FreeBSD and Linux).But be careful: Usually
/dev/randomprovides only as much entropy data as it actually has, i.e. when you request 512 bytes of entropy, but the device currently has only 100 bytes available two things can happen: On some platforms you receive only the 100 bytes while on other platforms the read blocks until enough bytes are available (which can take a long time). Here using an existing/dev/urandomis better, because it never blocks and actually gives the amount of requested data. The drawback is just that the quality of the received data may not be the best.On some platforms like FreeBSD one can even control how the entropy is actually generated, i.e. by which system interrupts. More details one can find under rndcontrol(8) on those platforms. Alternatively, when your system lacks such a random device, you can use tool like EGD (Entropy Gathering Daemon) and run it's client program with the
exec:/path/to/program/variant (see below) or useegd:/path/to/egd-socket(see below).exec:/path/to/programThis variant uses an external executable
/path/to/programas the source for seeding the PRNG. When bytes is specified, only the first bytes number of bytes of itsstdoutcontents form the entropy. When bytes is not specified, the entirety of the data produced onstdoutform the entropy. Use this only at startup time when you need a very strong seeding with the help of an external program (for instance as in the example above with thetruerandutility you can find in the mod_ssl distribution which is based on the AT&T truerand library). Using this in the connection context slows down the server too dramatically, of course. So usually you should avoid using external programs in that context.egd:/path/to/egd-socket(Unix only)This variant uses the Unix domain socket of the external Entropy Gathering Daemon (EGD) (see http://www.lothar.com/tech /crypto/) to seed the PRNG. Use this if no random device exists on your platform.
Example
SSLRandomSeed startup builtin
SSLRandomSeed startup file:/dev/random
SSLRandomSeed startup file:/dev/urandom 1024
SSLRandomSeed startup exec:/usr/local/bin/truerand 16
SSLRandomSeed connect builtin
SSLRandomSeed connect file:/dev/random
SSLRandomSeed connect file:/dev/urandom 1024
SSLRequire Directive
|
This directive specifies a general access requirement which has to be fulfilled in order to allow access. It's a very powerful directive because the requirement specification is an arbitrarily complex boolean expression containing any number of access checks.
The expression must match the following syntax (given as a BNF grammar notation):
expr ::= "true" | "false"
| "!" expr
| expr "&&" expr
| expr "||" expr
| "(" expr ")"
| comp
comp ::= word "==" word | word "eq" word
| word "!=" word | word "ne" word
| word "<" word | word "lt" word
| word "<=" word | word "le" word
| word ">" word | word "gt" word
| word ">=" word | word "ge" word
| word "in" "{" wordlist "}"
| word "=~" regex
| word "!~" regex
wordlist ::= word
| wordlist "," word
word ::= digit
| cstring
| variable
| function
digit ::= [0-9]+
cstring ::= "..."
variable ::= "%{" varname "}"
function ::= funcname "(" funcargs ")"
while for varname any variable from Table 3 can be used. Finally for
funcname the following functions are available:
file(filename)This function takes one string argument and expands to the contents of the file. This is especially useful for matching this contents against a regular expression, etc.
Notice that expression is first parsed into an internal machine representation and then evaluated in a second step. Actually, in Global and Per-Server Class context expression is parsed at startup time and at runtime only the machine representation is executed. For Per-Directory context this is different: here expression has to be parsed and immediately executed for every request.
Example
SSLRequire ( %{SSL_CIPHER} !~ m/^(EXP|NULL)-/ \
and %{SSL_CLIENT_S_DN_O} eq "Snake Oil, Ltd." \
and %{SSL_CLIENT_S_DN_OU} in {"Staff", "CA", "Dev"} \
and %{TIME_WDAY} >= 1 and %{TIME_WDAY} <= 5 \
and %{TIME_HOUR} >= 8 and %{TIME_HOUR} <= 20 ) \
or %{REMOTE_ADDR} =~ m/^192\.76\.162\.[0-9]+$/
|
SSLRequireSSL Directive
|
This directive forbids access unless HTTP over SSL (i.e. HTTPS) is enabled for the current connection. This is very handy inside the SSL-enabled virtual host or directories for defending against configuration errors that expose stuff that should be protected. When this directive is present all requests are denied which are not using SSL.
Example
SSLRequireSSL
SSLSessionCache Directive
|
This configures the storage type of the global/inter-process SSL Session Cache. This cache is an optional facility which speeds up parallel request processing. For requests to the same server process (via HTTP keep-alive), OpenSSL already caches the SSL session information locally. But because modern clients request inlined images and other data via parallel requests (usually up to four parallel requests are common) those requests are served by different pre-forked server processes. Here an inter-process cache helps to avoid unneccessary session handshakes.
The following two storage types are currently supported:
noneThis is the default and just disables the global/inter-process Session Cache. There is no drawback in functionality, but a noticeable speed penalty can be observed.
dbm:/path/to/datafileThis makes use of a DBM hashfile on the local disk to synchronize the local OpenSSL memory caches of the server processes. The slight increase in I/O on the server results in a visible request speedup for your clients, so this type of storage is generally recommended.
shm:/path/to/datafile[(size)]This makes use of a high-performance hash table (approx. size bytes in size) inside a shared memory segment in RAM (established via
/path/to/datafile) to synchronize the local OpenSSL memory caches of the server processes. This storage type is not available on all platforms. See the mod_sslINSTALLdocument for details on how to build Apache+EAPI with shared memory support.
Examples
SSLSessionCache dbm:/usr/local/apache/logs/ssl_gcache_data
SSLSessionCache shm:/usr/local/apache/logs/ssl_gcache_data(512000)
SSLSessionCacheTimeout Directive
|
This directive sets the timeout in seconds for the information stored in the global/inter-process SSL Session Cache and the OpenSSL internal memory cache. It can be set as low as 15 for testing, but should be set to higher values like 300 in real life.
Example
SSLSessionCacheTimeout 600
SSLVerifyClient Directive
|
This directive sets the Certificate verification level for the Client Authentication. Notice that this directive can be used both in per-server and per-directory context. In per-server context it applies to the client authentication process used in the standard SSL handshake when a connection is established. In per-directory context it forces a SSL renegotation with the reconfigured client verification level after the HTTP request was read but before the HTTP response is sent.
The following levels are available for level:
- none: no client Certificate is required at all
- optional: the client may present a valid Certificate
- require: the client has to present a valid Certificate
- optional_no_ca:
the client may present a valid Certificate
but it need not to be (successfully) verifiable.
In practice only levels none and require are really interesting, because level optional doesn't work with all browsers and level optional_no_ca is actually against the idea of authentication (but can be used to establish SSL test pages, etc.)
Example
SSLVerifyClient require
SSLVerifyDepth Directive
|
This directive sets how deeply mod_ssl should verify before deciding that the clients don't have a valid certificate. Notice that this directive can be used both in per-server and per-directory context. In per-server context it applies to the client authentication process used in the standard SSL handshake when a connection is established. In per-directory context it forces a SSL renegotation with the reconfigured client verification depth after the HTTP request was read but before the HTTP response is sent.
The depth actually is the maximum number of intermediate certificate issuers,
i.e. the number of CA certificates which are max allowed to be followed while
verifying the client certificate. A depth of 0 means that self-signed client
certificates are accepted only, the default depth of 1 means the client
certificate can be self-signed or has to be signed by a CA which is directly
known to the server (i.e. the CA's certificate is under
SSLCACertificatePath), etc.
Example
SSLVerifyDepth 10
