netcdf-c/docs/auth.html

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<h1 class="title">netCDF Authorization Support</h1> 
<div class="subtitle">
<h1>Author: Dennis Heimbigner</h1>
<h1>Address: http://www.unidata.ucar.edu/staff/dmh/</h1>
<h1>Draft: 11/21/2014</h1>
<h1>Last Revised: 10/24/2015</h1>
</div>
 
<h1 class="toc">Table of Contents</h1> 
<ol> 
<li> <a href="#Introduction">Introduction</a> 
<li> <a href="#URL-AUTH">URL-Based Authentication</a> 
<li> <a href="#DODSRC">RC File Authentication</a> 
<li> <a href="#REDIR">Redirection-Based Authentication</a> 
<li> <a href="#URLCONS">URL Constrained RC File Entries</a> 
<li> <a href="#CLIENTCERTS">Client-Side Certificates</a> 
<li> <a href="#allkeys">Appendix A. All RC-File Keys</a>
<li> <a href="#ESGDETAIL">Appendix B. ESG Access in Detail</a>
</ol> 
 
<h2><a name="Introduction">Introduction</a></h2> 
netCDF can support user authorization using the facilities provided by the curl
library. This includes basic password authentication as well as
certificate-based authorization.
<p>
At the moment, this document only applies to DAP2 and DAP4 access
because they are (for now) the only parts of the netCDF-C library
that uses libcurl.
<p>
With some exceptions (e.g. see the section on <a href="#REDIR">redirection</a>)
The libcurl authorization mechanisms can be accessed in two ways
<ol>
<li> Inserting the username and password into the url, or
<li> Accessing information from a so-called <i>rc</i> file named either
<i>.daprc</i> or <i>.dodsrc</i>
</ol>

<h2><a name="URL-AUTH">URL-Based Authentication</a></h2> 
For simple password based authentication, it is possible to
directly insert the username and the password into a url in this form.
<pre>
    http://username:password@host/...
</pre>
This username and password will be used if the server asks for
authentication. Note that only simple password authentication
is supported in this format.
Specifically note that <a href="#REDIR">redirection</a> based
authorization will not work with this because the username and password
will only be used on the initial request, not the redirection

<h2><a name="DODSRC">RC File Authentication</a></h2> 
The netcdf library supports an <i>rc</i> file mechanism to allow the passing
of a number of parameters to libnetcdf and libcurl.
<p>
The file must be called one of the following names:
".daprc" or ".dodsrc"
If both .daprc and .dodsrc exist, then
the .daprc file will take precedence.
<p>
The rc file is searched for first in the current directory
and then in the home directory (as defined by the HOME environment
variable).
<p>
The rc file format is a series of lines of the general form:
<pre>
[&lt;host:port&gt;]&lt;key&gt;=&lt;value&gt;
</pre>
where the bracket-enclosed host:port is optional and will be discussed 
subsequently.
<p>
The currently defined set of authorization-related keys are as follows.
The second column is the affected curl_easy_setopt option(s), if any.
<table>
<tr><th>Key<th>Affected curl_easy_setopt Options<th>Notes
<tr><td>HTTP.COOKIEJAR<td>CURLOPT_COOKIEJAR
<tr><td>HTTP.COOKIEFILE<td>CURLOPT_COOKIEJAR<td>Alias for CURLOPT_COOKIEJAR
<tr><td>HTTP.PROXY_SERVER<td>CURLOPT_PROXY, CURLOPT_PROXYPORT, CURLOPT_PROXYUSERPWD
<tr><td>HTTP.SSL.CERTIFICATE<td>CURLOPT_SSLCERT
<tr><td>HTTP.SSL.KEY<td>CURLOPT_SSLKEY
<tr><td>HTTP.SSL.KEYPASSWORD<td>CURLOPT_KEYPASSWORD
<tr><td>HTTP.SSL.CAINFO<td>CURLOPT_SSLCAINFO
<tr><td>HTTP.SSL.CAPATH<td>CURLOPT_SSLCAPATH
<tr><td>HTTP.SSL.VERIFYPEER<td>CURLOPT_SSL_VERIFYPEER
<tr><td>HTTP.SSL.VALIDATE<td>CURLOPT_SSL_VERIFYPEER, CURLOPT_SSL_VERIFYHOST
<tr><td>HTTP.CREDENTIALS.USERPASSWORD<td>CURLOPT_USERPASSWORD
<tr><td>HTTP.NETRC<td>N.A.<td>Specify path of the .netrc file
</table>
</ul>

<h3>Password Authentication</h3> 
The key
HTTP.CREDENTIALS.USERPASSWORD
can be used to set the simple password authentication.
This is an alternative to setting it in the url. 
The value must be of the form "username:password".
See <a href="#REDIR">redirection authorization</a>
for important additional information.

<h3>Cookie Jar</h3> 
The HTTP.COOKIEJAR key
specifies the name of file from which
to read cookies (CURLOPT_COOKIEJAR) and also
the file into which to store cookies (CURLOPT_COOKIEFILE).
The same value is used for both CURLOPT values.
It defaults to in-memory storage.
See <a href="#REDIR">redirection authorization</a>
for important additional information.

<h3>Certificate Authentication</h3> 
HTTP.SSL.CERTIFICATE
specifies a file path for a file containing a PEM cerficate.
This is typically used for client-side authentication.
<p>
HTTP.SSL.KEY is essentially the same as HTTP.SSL.CERTIFICATE
and should always have the same value.
<p>
HTTP.SSL.KEYPASSWORD
specifies the password for accessing the HTTP.SSL.CERTIFICAT/HTTP.SSL.key file.
<p>
HTTP.SSL.CAPATH
specifies the path to a directory containing
trusted certificates for validating server certificates.
<p>
HTTP.SSL.VALIDATE
is a boolean (1/0) value that if true (1)
specifies that the client should verify the server's presented certificate.
<p>
HTTP.PROXY_SERVER
specifies the url for accessing the proxy:
e.g. <i>http://[username:password@]host[:port]</i>
<p>
HTTP.NETRC
specifies the absolute path of the .netrc file.
See <a href="#REDIR">redirection authorization</a>
for information about using .netrc.

<h2><a name="REDIR">Redirection-Based Authentication</a> </h2>
Some sites provide authentication by using a third party site
to do the authentication. Examples include ESG and URS.
<p>
The process is usually as follows.
<ol>
<li>The client contacts the server of interest (SOI), the actual data provider
using, typically http protocol.
<li>The SOI sends a redirect to the client to connect to the e.g. URS system
using the 'https' protocol (note the use of https instead of http).
<li>The client authenticates with URS.
<li>URS sends a redirect (with authorization information) to send
the client back to the SOI to actually obtain the data.
</ol>
<p>
It turns out that libcurl uses the password in the .daprc file &mdash; or from the url &mdash;
only for the initial connection. This causes problems because
the redirected connection is the one that actually requires the password.
This is where .netrc comes in. Libcurl will use .netrc for
the redirected connection. It is possible to cause libcurl to use
the .daprc password always, but this introduces a security hole
because it may send the initial user+pwd to the redirection site.
In summary, if you are using redirection, then you must create a .netrc
file to hold the password for the site to which the redirection is sent.
<p>
The format of this .netrc file will contain content that
typically look like this.
<pre>
machine mmmmmm login xxxxxx password yyyyyy
</pre>
where the machine, mmmmmm, is the hostname of the machine to
which the client is redirected for authorization, and the
login and password are those needed to authenticate on that machine.
<p>
The .netrc file can be specified by
putting the following line in your .daprc/.dodsrc file.
<pre>
HTTP.NETRC=&lt;path to netrc file&gt;
</pre>

<p>
One final note. In using this, it is almost certain that you will
need to specify a real cookie jar file (HTTP.COOKIEJAR) so that the
redirect site can pass back authorization information.

<h2><a name="URLCONS">URL Constrained RC File Entries</a></h2> 
Each line of the rc file can begin with
a host+port enclosed in square brackets.
The form is "host:port". 
If the port is not specified
then the form is just "host".
The reason that more of the url is not used is that
libcurl's authorization grain is not any finer than host level.
<p>
Examples.
<pre>
[remotetest.unidata.ucar.edu]HTTP.VERBOSE=1
or
[fake.ucar.edu:9090]HTTP.VERBOSE=0
</pre>
If the url request from, say, the <i>netcdf_open</i> method
has a host+port matching one of the prefixes in the rc file, then
the corresponding entry will be used, otherwise ignored.
<p>
For example, the URL
<pre>
http://remotetest.unidata.ucar.edu/thredds/dodsC/testdata/testData.nc
</pre>
will have HTTP.VERBOSE set to 1.
<p>
Similarly, 
<pre>
http://fake.ucar.edu:9090/dts/test.01
</pre>
will have HTTP.VERBOSE set to 0.

<h2><a name="CLIENTCERTS">Client-Side Certificates</a></h2> 
Some systems, notably ESG (Earth System Grid), requires
the use of client-side certificates, as well as being
<a href="#REDIR">re-direction based</a>.
This requires setting the following entries:
<ul>
<li>HTTP.COOKIEJAR &mdash; a file path for storing cookies across re-direction.
<li>HTTP.NETRC &mdash; the path to the netrc file.
<li>HTTP.SSL.CERTIFICATE &mdash; the file path for the client side certificate file.
<li>HTTP.SSL.KEY &mdash; this should have the same value as HTTP.SSL.CERTIFICATE.
<li>HTTP.SSL.CAPATH &mdash; the path to a "certificates" directory.
<li>HTTP.SSL.VALIDATE &mdash; force validation of the server certificate.
</ul>
Note that the first two are to support re-direction based authentication.

<h1 class="appendix><a name="allkeys">Appendix A. All RC-File Keys</a></h1> 
For completeness, this is the list of all rc-file keys.
If this documentation is out of date with respect to the actual code,
the code is definitive.
<table>
<tr><th>Key<th>curl_easy_setopt Option
<tr valign="top"><td>HTTP.DEFLATE<td>CUROPT_DEFLATE<br>with value "deflate,gzip"
<tr><td>HTTP.VERBOSE <td>CUROPT_VERBOSE 
<tr><td>HTTP.TIMEOUT<td>CUROPT_TIMEOUT
<tr><td>HTTP.USERAGENT<td>CUROPT_USERAGENT
<tr><td>HTTP.COOKIEJAR<td>CUROPT_COOKIEJAR
<tr><td>HTTP.COOKIE_JAR<td>CUROPT_COOKIEJAR
<tr valign="top"><td>HTTP.PROXY_SERVER<td>CURLOPT_PROXY,<br>CURLOPT_PROXYPORT,<br>CURLOPT_PROXYUSERPWD
<tr><td>HTTP.SSL.CERTIFICATE<td>CUROPT_SSLCERT
<tr><td>HTTP.SSL.KEY<td>CUROPT_SSLKEY
<tr><td>HTTP.SSL.KEYPASSWORD<td>CUROPT_KEYPASSWORD
<tr><td>HTTP.SSL.CAINFO<td>CUROPT_SSLCAINFO
<tr><td>HTTP.SSL.CAPATH<td>CUROPT_SSLCAPATH
<tr><td>HTTP.SSL.VERIFYPEER<td>CUROPT_SSL_VERIFYPEER
<tr><td>HTTP.CREDENTIALS.USERPASSWORD<td>CUROPT_USERPASSWORD
<tr><td>HTTP.NETRC<td>CURLOPT_NETRC,CURLOPT_NETRC_FILE
</table>
</ul>

<h1 class="appendix"><a name="URSDETAIL">Appendix B. URS Access in Detail</a></h1>
It is possible to use the NASA Earthdata Login System (URS)
with netcdf by using using the process specified in the 
<a href="#REDIR">redirection</a> based authorization section.
In order to access URS controlled datasets, however, it is necessary to
register as a user with NASA at the
<i>https://uat.urs.earthdata.nasa.gov/</i>
website.

<h1 class="appendix"><a name="ESGDETAIL">Appendix C. ESG Access in Detail</a></h1>
It is possible to access Earth Systems Grid (ESG) datasets
from ESG servers through the netCDF API using the techniques
described in the section on <a href="#CLIENTCERTS">Client-Side Certificates</a>.
<p>
In order to access ESG datasets, however, it is necessary to
register as a user with ESG and to setup your environment
so that proper authentication is established between an netcdf
client program and the ESG data server.  Specifically, it
is necessary to use what is called "client-side keys" to
enable this authentication. Normally, when a client accesses
a server in a secure fashion (using "https"), the server
provides an authentication certificate to the client.
With client-side keys, the client must also provide a
certificate to the server so that the server can know with
whom it is communicating.
<p>
The netcdf library uses the <i>curl</i> library and it is that
underlying library that must be properly configured.

<h3>Terminology</h3>
The key elements for client-side keys requires the constructions of
two "stores" on the client side.
<ul>
<li> Keystore - a repository to hold the client side key.
<li> Truststore - a repository to hold a chain of certificates
                  that can be used to validate the certificate
		  sent by the server to the client.
</ul>
The server actually has a similar set of stores, but the client
need not be concerned with those.

<h3>Initial Steps</h3>

The first step is to obtain authorization from ESG.
Note that this information may evolve over time, and
may be out of date.
This discussion is in terms of BADC and NCSA. You will need
to substitute as necessary.
<ol>
<li> Register at http://badc.nerc.ac.uk/register
   to obtain access to badc and to obtain an openid,
   which will looks something like:
   <pre>https://ceda.ac.uk/openid/Firstname.Lastname</pre>
<li> Ask BADC for access to whatever datasets are of interest.
<p>
<li> Obtain short term credentials at
   http://grid.ncsa.illinois.edu/myproxy/MyProxyLogon/
   You will need to download and run the MyProxyLogon
   program.
   This will create a keyfile in, typically, the directory ".globus".
   The keyfile will have a name similar to this: "x509up_u13615"
   The other elements in ".globus" are certificates to use in
   validating the certificate your client gets from the server.
<p>
<li> Obtain the program source ImportKey.java
   from this location: http://www.agentbob.info/agentbob/79-AB.html
   (read the whole page, it will help you understand the remaining steps).
</ol>

<h3>Building the KeyStore</h3>
You will have to modify the keyfile in the previous step
and then create a keystore and install the key and a certificate.
The commands are these:
<pre>
    openssl pkcs8 -topk8 -nocrypt -in x509up_u13615 -inform PEM -out key.der -outform DER

    openssl x509 -in x509up_u13615 -inform PEM -out cert.der -outform DER

    java -classpath <path to ImportKey.class> -Dkeypassword="<password>" -Dkeystore=./<keystorefilename> key.der cert.der
</pre>     
Note, the file names "key.der" and "cert.der" can be whatever you choose.
It is probably best to leave the .der extension, though.

<h3>Building the TrustStore</h3>
Building the truststore is a bit tricky because as provided, the
certificates in ".globus" need some massaging. See the script below
for the details. The primary command is this, which is executed for every
certificate, c, in globus. It sticks the certificate into the file
named "truststore"
<pre>
  keytool -trustcacerts -storepass "password" -v -keystore "truststore"  -importcert -file "${c}"
</pre>

<h3>Running the C Client</h3>

Refer to the section on <a href="#CLIENTCERTS">Client-Side Certificates</a>.
The keys specified there  must be set in the rc file to support
ESG access.
<ul>
<li> HTTP.COOKIEJAR=~/.dods_cookies
<li> HTTP.NETRC=~/.netrc
<li> HTTP.SSL.CERTIFICATE=~/esgkeystore
<li> HTTP.SSL.KEY=~/esgkeystore
<li> HTTP.SSL.CAPATH=~/.globus
<li> HTTP.SSL.VALIDATE=1
</ul>
Of course, the file paths above are suggestions only;
you can modify as needed.
The HTTP.SSL.CERTIFICATE and HTTP.SSL.KEY
entries should have same value, which is the file path for the
certificate produced by MyProxyLogon.  The HTTP.SSL.CAPATH entry
should be the path to the "certificates" directory produced by
MyProxyLogon.
<p>
As noted, also uses re-direction based authentication.
So, when it receives an initial connection from a client, it
redirects to a separate authentication server. When that
server has authenticated the client, it redirects back to
the original url to complete the request.

<h3>Script for creating Stores</h3>
The following script shows in detail how to actually construct the key
and trust stores. It is specific to the format of the globus file
as it was when ESG support was first added. It may have changed
since then, in which case, you will need to seek some help
in fixing this script. It would help if you communicated
what you changed to the author so this document can be updated.
<pre>
#!/bin/sh -x
KEYSTORE="esgkeystore"
TRUSTSTORE="esgtruststore"
GLOBUS="globus"
TRUSTROOT="certificates"
CERT="x509up_u13615"
TRUSTROOTPATH="$GLOBUS/$TRUSTROOT"
CERTFILE="$GLOBUS/$CERT"
PWD="password"

D="-Dglobus=$GLOBUS"
CCP="bcprov-jdk16-145.jar" 
CP="./build:${CCP}" 
JAR="myproxy.jar"

# Initialize needed directories
rm -fr build
mkdir build
rm -fr $GLOBUS
mkdir $GLOBUS
rm -f $KEYSTORE
rm -f $TRUSTSTORE

# Compile MyProxyCmd and ImportKey
javac -d ./build -classpath "$CCP" *.java
javac -d ./build ImportKey.java

# Execute MyProxyCmd
java -cp "$CP myproxy.MyProxyCmd

# Build the keystore
openssl pkcs8 -topk8 -nocrypt -in $CERTFILE -inform PEM -out key.der -outform DER
openssl x509 -in $CERTFILE -inform PEM -out cert.der -outform DER
java -Dkeypassword=$PWD -Dkeystore=./${KEYSTORE} -cp ./build ImportKey key.der cert.der

# Clean up the certificates in the globus directory
for c in ${TRUSTROOTPATH}/*.0 ; do
    alias=`basename $c .0`
    sed -e '0,/---/d' <$c >/tmp/${alias}
    echo "-----BEGIN CERTIFICATE-----" >$c       
    cat /tmp/${alias} >>$c
done
 
# Build the truststore
for c in ${TRUSTROOTPATH}/*.0 ; do
    alias=`basename $c .0`
    echo "adding: $TRUSTROOTPATH/${c}"
    echo "alias: $alias"
    yes | keytool -trustcacerts -storepass "$PWD" -v -keystore ./$TRUSTSTORE -alias $alias -importcert -file "${c}"
done
exit
</pre>

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