netcdf-c/docs/auth.md

Authorization Support in the netCDF-C Libraries

\brief It is possible to support a number of authorization schemes in the netCDF-C library.

With one exception, authorization in the netCDF-C library is delegated to the oc2 code, which in turn delegates it to the libcurl library. The exception is that the location of the rc file can be specified by setting the environment variable NCRCFILE. Note that the value of this environment variable should be the absolute path of the rc file, not the path to its containing directory.

Following is the authorization documentation.

OC Authorization Support

Author: Dennis Heimbigner
dmh at ucar dot edu

Draft: 11/21/2014
Last Revised: 12/23/2014
OC Version 2.1

Table of Contents

1. Introduction
2. URL-Based Authentication
3. RC File Authentication
4. Redirection-Based Authentication
5. URL Constrained RC File Entries
6. Client-Side Certificates
7. Appendix A. All RC-File Keys
8. Appendix B. ESG Access in Detail

Introduction

OC can support user authorization using those provided by the curl library. This includes basic password authentication as well as certificate-based authorization.

With some exceptions (e.g. see the section on redirection) The libcurl authorization mechanisms can be accessed in two ways

1. Inserting the username and password into the url, or
2. Accessing information from a so-called rc file named either .daprc or .dodsrc

URL-Based Authentication

For simple password based authentication, it is possible to directly insert the username and the password into a url in this form.

    http://username:password@host/...

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 redirection based authorization will not work with this.

RC File Authentication

The oc library supports an rc file mechanism to allow the passing of a number of parameters to liboc and libcurl.

The file must be called one of the following names: ".daprc", ".dodsrc" If both .daprc and .dodsrc exist, then the .daprc file will take precedence.

Searching for the rc file first looks in the current directory and then in the home directory (as defined by the HOME environment variable). It is also possible to specify a direct path using the -R option to ocprint or using the oc_set_rcfile procedure (see oc.h). Note that for these latter cases, the path must be to the file itself, not to the containing directory.

The rc file format is a series of lines of the general form:

[<host:port>]<key>=<value>

where the bracket-enclosed host:port is optional and will be discussed subsequently.

The currently defined set of authorization-related keys are as follows. The second column is the affected curl_easy_setopt option(s).

Key

curl_easy_setopt Option

HTTP.COOKIEJAR

CURLOPT_COOKIEJAR, CURLOPT_COOKIEFILE

HTTP.PROXY_SERVER

CURLOPT_PROXY, CURLOPT_PROXYPORT, CURLOPT_PROXYUSERPWD

HTTP.SSL.CERTIFICATE

CURLOPT_SSLCERT

HTTP.SSL.KEY

CURLOPT_SSLKEY

HTTP.SSL.KEYPASSWORD

CURLOPT_KEYPASSWORD

HTTP.SSL.CAINFO

CURLOPT_SSLCAINFO

HTTP.SSL.CAPATH

CURLOPT_SSLCAPATH

HTTP.SSL.VERIFYPEER

CURLOPT_SSL_VERIFYPEER

HTTP.CREDENTIALS.USERPASSWORD

CURLOPT_USERPASSWORD

Password Authentication

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".

Cookie Jar

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.

Certificate Authentication

HTTP.SSL.CERTIFICATE specifies a file path for a file containing a PEM cerficate. This is typically used for client-side authentication.

HTTP.SSL.KEY is essentially the same as HTTP.SSL.CERTIFICATE and should usually have the same value.

HTTP.SSL.KEYPASSWORD specifies the password for accessing the HTTP.SSL.KEY/HTTP.SSL.CERTIFICATE file.

HTTP.SSL.CAPATH specifies the path to a directory containing trusted certificates for validating server sertificates.

HTTP.SSL.VALIDATE is a boolean (1/0) value that if true (1) specifies that the client should verify the server's presented certificate.

HTTP.PROXY_SERVER specified the url for accessing the proxy: (e.g.http://[username:password@]host[:port])

Redirection-Based Authentication

Some sites provide authentication by using a third party site to to the authentication. One example is URS, the EOSDIS User Registration System.

The process is usually as follows.

1. The client contacts the server of interest (SOI), the actual data provider.
2. The SOI sends a redirect to the client to connect to the URS system.
3. The client authenticates with URS.
4. URS sends a redirect (with authorization information) to send the client back to the SOI to actually obtain the data.

In order for this to work with libcurl, the client will usually need to provide a .netrc file so that the redirection will work correctly. The format of this .netrc file will contain content that typically look like this.

machine uat.urs.earthdata.nasa.gov login xxxxxx password yyyyyy

where the machine is the one to which the client is redirected for authorization, and the login and password are those needed to authenticate.

The .netrc file can be specified in two ways.

1. Specify the netrc file to liboc using the procedure in oc.h:

   oc_set_netrc(OClink* link, const char* file)
   

   (This is equivalent to the -N flag to ocprint).

2. Put the following line in your .daprc/.dodsrc file.

   HTTP.NETRC=<path to netrc file>
   

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

URL Constrained RC File Entries

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.

Examples.

[remotetest.unidata.ucar.edu]HTTP.VERBOSE=1
or
[fake.ucar.edu:9090]HTTP.VERBOSE=0

If the url request from, say, the oc_open method has a host+port matchine one of the prefixes in the rc file, then the corresponding entry will be used, otherwise ignored.

For example, the URL

http://remotetest.unidata.ucar.edu/thredds/dodsC/testdata/testData.nc

will have HTTP.VERBOSE set to 1.

Similarly,

http://fake.ucar.edu:9090/dts/test.01

will have HTTP.VERBOSE set to 0.

Client-Side Certificates

Some systems, notably ESG (Earth System Grid), requires the use of client-side certificates, as well as being re-direction based. This requires setting the following entries:

• HTTP.COOKIEJAR — a file path for storing cookies across re-direction.
• HTTP.NETRC — the path to the netrc file.
• HTTP.SSL.CERTIFICATE — the file path for the client side certificate file.
• HTTP.SSL.KEY — this should have the same value as HTTP.SSL.CERTIFICATE.
• HTTP.SSL.CAPATH — the path to a "certificates" directory.
• HTTP.SSL.VALIDATE — force validation of the server certificate.

Note that the first two are to support re-direction based authentication.

Appendix A. All RC-File Keys

For completeness, this is the list of all rc-file keys.

Key

curl_easy_setopt Option

HTTP.DEFLATE

CUROPT_DEFLATE
with value "deflate,gzip"

HTTP.VERBOSE

CUROPT_VERBOSE

HTTP.TIMEOUT

CUROPT_TIMEOUT

HTTP.USERAGENT

CUROPT_USERAGENT

HTTP.COOKIEJAR

CUROPT_COOKIEJAR

HTTP.COOKIE_JAR

CUROPT_COOKIEJAR

HTTP.PROXY_SERVER

CURLOPT_PROXY,
CURLOPT_PROXYPORT,
CURLOPT_PROXYUSERPWD

HTTP.SSL.CERTIFICATE

CUROPT_SSLCERT

HTTP.SSL.KEY

CUROPT_SSLKEY

HTTP.SSL.KEYPASSWORD

CUROPT_KEYPASSWORD

HTTP.SSL.CAINFO

CUROPT_SSLCAINFO

HTTP.SSL.CAPATH

CUROPT_SSLCAPATH

HTTP.SSL.VERIFYPEER

CUROPT_SSL_VERIFYPEER

HTTP.CREDENTIALS.USERPASSWORD

CUROPT_USERPASSWORD

HTTP.NETRC

CURLOPT_NETRC,CURLOPT_NETRC_FILE

Appendix B. ESG Access in Detail

It is possible to access Earth Systems Grid (ESG) datasets from ESG servers through the OC API using the techniques described in the section on Client-Side Certificates.

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 oc 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.

The oc library uses the curl library and it is that underlying library that must be properly configured.

Terminology

The key elements for client-side keys requires the constructions of two "stores" on the client side.

• Keystore - a repository to hold the client side key.
• Truststore - a repository to hold a chain of certificates that can be used to validate the certificate sent by the server to the client.

The server actually has a similar set of stores, but the client need not be concerned with those.

Initial Steps

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.

1. Register at http://badc.nerc.ac.uk/register to obtain access to badc and to obtain an openid, which will looks something like:

   https://ceda.ac.uk/openid/Firstname.Lastname
   

2. Ask BADC for access to whatever datasets are of interest.

3. 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.

4. 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).

Building the KeyStore

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:

    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  -Dkeypassword="" -Dkeystore=./ key.der cert.der

Note, the file names "key.der" and "cert.der" can be whatever you choose. It is probably best to leave the .der extension, though.

Building the TrustStore

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"

  keytool -trustcacerts -storepass "password" -v -keystore "truststore"  -importcert -file "${c}"

Running the C Client

Refer to the section on Client-Side Certificates. The keys specified there must be set in the rc file to support ESG access.

• HTTP.COOKIEJAR=~/.dods_cookies
• HTTP.NETRC=~/.netrc
• HTTP.SSL.CERTIFICATE=~/esgkeystore
• HTTP.SSL.KEY=~/esgkeystore
• HTTP.SSL.CAPATH=~/.globus
• HTTP.SSL.VALIDATE=1

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.

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.

Script for creating Stores

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.

#!/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