Add README configuration section

This adds details about how to control which BMCWeb features are
enabled at build time, and how persistent configuration data and
SSL certificates and handled.

Tested: N/A

Change-Id: Id0fc6617da859468e433f2038e9aaf4645c99ab0
Signed-off-by: Joseph Reynolds <jrey@us.ibm.com>

1 files changed, 21 insertions, 1 deletions

diff --git a/README.md b/README.md
index 080e85a374..77ac92e71a 100644
--- a/README.md
+++ b/README.md
@@ -9,10 +9,30 @@ At this time, the webserver implements a few interfaces:
 + An (incomplete) attempt at replicating phosphor-dbus-rest interfaces in C++.  Right now, a few of the endpoint definitions work as expected, but there is still a lot of work to be done.  The portions of the interface that are functional are designed to work correctly for phosphor-webui, but may not yet be complete.
 + Replication of the rest-dbus backend interfaces to allow bmc debug to logged in users.
 + An initial attempt at a read-only redfish interface.  Currently the redfish interface targets ServiceRoot, SessionService, AccountService, Roles, and ManagersService.  Some functionality here has been shimmed to make development possible.  For example, there exists only a single user role.
-+ SSL key generation at runtime.  If an RSA key and cert pair are not available to the server at runtime, keys are generated using the openssl routines, and written to disk.
++ SSL key generation at runtime.  See the configuration section for details.
 + Static file hosting.  Currently, static files are hosted from the fixed location at /usr/share/www.  This is intended to allow loose coupling with yocto projects, and allow overriding static files at build time.
 + Dbus-monitor over websocket.  A generic endpoint that allows UIs to open a websocket and register for notification of events to avoid polling in single page applications.  (this interface may be modified in the future due to security concerns.
 
+## Configuration
+
+BMCWeb is configured by setting `-D` flags that correspond to options
+in `bmcweb/CMakeLists.txt` and then compiling.  For example, `cmake
+-DBMCWEB_ENABLE_KVM=NO ...` followed by `make`.  The option names
+become C++ preprocessor symbols that control which code is compiled
+into the program.
+
+When BMCWeb starts running, it reads persistent configuration data
+(such as UUID and session data) from a local file.  If this is not
+usable, it generates a new configuration.
+
+When BMCWeb SSL support is enabled and a usable certificate is not
+found, it will generate a self-sign a certificate before launching the
+server.  The keys are generated by the `prime256v1` algorithm.  The
+certificate
+ - is issued by `C=US, O=Intel BMC, CN=testhost`,
+ - is valid for 10 years,
+ - has a random serial number, and
+ - is signed using the `SHA-256` algorithm.
 
 ## Crow patches ##
 The crow project has had a number of additions to make it more useful for use in the OpenBmc Project.  A non-exhaustive list is below.  At the time of this writing, the crow project is not accepting patches, so for the time being crow will simply be checked in as is.