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Add package starformer, uses Starlark for user-defined authn filters

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This commit is contained in:
Ryan Richard 2023-02-01 10:49:38 -08:00
parent 60d12d88ac
commit aa57a5150e
4 changed files with 546 additions and 0 deletions
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1
go.mod
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@ -30,6 +30,7 @@ require (
github.com/spf13/pflag v1.0.5
github.com/stretchr/testify v1.8.1
github.com/tdewolff/minify/v2 v2.12.4
go.starlark.net v0.0.0-20210602144842-1cdb82c9e17a
go.uber.org/zap v1.24.0
golang.org/x/crypto v0.5.0
golang.org/x/net v0.5.0

2
go.sum
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@ -613,6 +613,8 @@ go.opentelemetry.io/otel/trace v1.10.0/go.mod h1:Sij3YYczqAdz+EhmGhE6TpTxUO5/F/A
go.opentelemetry.io/proto/otlp v0.7.0/go.mod h1:PqfVotwruBrMGOCsRd/89rSnXhoiJIqeYNgFYFoEGnI=
go.opentelemetry.io/proto/otlp v0.19.0 h1:IVN6GR+mhC4s5yfcTbmzHYODqvWAp3ZedA2SJPI1Nnw=
go.opentelemetry.io/proto/otlp v0.19.0/go.mod h1:H7XAot3MsfNsj7EXtrA2q5xSNQ10UqI405h3+duxN4U=
go.starlark.net v0.0.0-20210602144842-1cdb82c9e17a h1:wDtSCWGrX9tusypq2Qq9xzaA3Tf/+4D2KaWO+HQvGZE=
go.starlark.net v0.0.0-20210602144842-1cdb82c9e17a/go.mod h1:t3mmBBPzAVvK0L0n1drDmrQsJ8FoIx4INCqVMTr/Zo0=
go.uber.org/atomic v1.4.0/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
go.uber.org/atomic v1.10.0 h1:9qC72Qh0+3MqyJbAn8YU5xVq1frD8bn3JtD2oXtafVQ=

183
internal/starformer/starformer.go Normal file
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@ -0,0 +1,183 @@
// Copyright 2021 the Pinniped contributors. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
// Package starformer is an implementation of UpstreamToDownstreamTransformer using Starlark scripts.
// See Starlark dialect language documentation here: https://github.com/google/starlark-go/blob/master/doc/spec.md
// A video introduction to Starlark and how to integrate it into projects is here: https://www.youtube.com/watch?v=9P_YKVhncWI
package starformer
import (
"fmt"
"go.starlark.net/lib/json"
starlarkmath "go.starlark.net/lib/math"
"go.starlark.net/lib/time"
"go.starlark.net/resolve"
"go.starlark.net/starlark"
"go.pinniped.dev/internal/plog"
)
const (
maxExecutionSteps = 10000000
transformFunctionName = "transform"
)
// Configure some global variables in starlark-go.
// nolint:gochecknoinits // wish these weren't globals but oh well
func init() {
// Allow the non-standard "set" data structure to be used.
resolve.AllowSet = true
// Note that we could allow "while" statements and recursive functions, but the language already
// has "for" loops so it seems unnecessary for our use case. This is currently the default
// value in starlark-go but repeating it here as documentation.
resolve.AllowRecursion = false
}
type Transformer struct {
hook *starlark.Function
}
// New creates an instance of Transformer. Given some Starlark source code as a string, it loads the code.
// If there is any error during loading, it will return the error. It expects the loaded code to define
// a Starlark function called "transform" which should take two positional arguments. The returned
// Transformer can be safely called from multiple threads simultaneously, no matter how the Starlark
// source code was written, because the Starlark module has been frozen (made immutable).
func New(starlarkSourceCode string) (*Transformer, error) {
// Create a Starlark thread in which the source will be loaded.
thread := &starlark.Thread{
Name: "starlark script loader",
Print: func(thread *starlark.Thread, msg string) {
// When the script has a top-level print(), send it to the server log.
plog.Debug("debug message while loading starlark transform script", "msg", msg)
},
Load: func(thread *starlark.Thread, module string) (starlark.StringDict, error) {
// Allow starlark-go's custom built-in modules to be loaded by scripts if they desire.
switch module {
case "json.star":
return starlark.StringDict{"json": json.Module}, nil
case "time.star":
return starlark.StringDict{"time": time.Module}, nil
case "math.star":
return starlark.StringDict{"math": starlarkmath.Module}, nil
default:
// Don't allow any other file to be loaded.
return nil, fmt.Errorf("only the following modules may be loaded: json.star, time.star, math.star")
}
},
}
// Prevent the top-level statements of the Starlark script from accidentally running forever.
thread.SetMaxExecutionSteps(maxExecutionSteps)
// Start with empty predeclared names, aside from the built-ins.
predeclared := starlark.StringDict{}
// Load a Starlark script. Initialization of a script runs its top-level statements from top to bottom,
// and then "freezes" all of the values making them immutable. The result can be used in multiple threads
// simultaneously without interfering, communicating, or racing with each other. The filename given here
// will appear in some Starlark error messages.
globals, err := starlark.ExecFile(thread, "transform.star", starlarkSourceCode, predeclared)
if err != nil {
return nil, fmt.Errorf("error while loading starlark transform script: %w", err)
}
// Get the function called "transform" from the global state of the module that was just loaded.
hook, _ := globals[transformFunctionName].(*starlark.Function)
if hook == nil {
return nil, fmt.Errorf("starlark script does not define %q function", transformFunctionName)
}
// Check that the "transform" function takes the expected number of arguments so we can call it later.
if hook.NumParams() != 2 {
return nil, fmt.Errorf("starlark script's global %q function has %d parameters but should have 2", transformFunctionName, hook.NumParams())
}
return &Transformer{hook: hook}, nil
}
// Transform calls the Starlark "transform" function that was loaded by New. The username and groups params are
// passed into the Starlark function, and the return values of the Starlark function are returned. If there is an error
// during the call to the Starlark function (either a programming error, a runtime error, or an intentional call to
// Starlark's `fail` built-in function) then Transform will return the error. This function is thread-safe.
// The runtime of this function depends on the complexity of the Starlark source code, but for a typical Starlark
// function will be something on the order of 50µs on a modern laptop.
func (t *Transformer) Transform(username string, groups []string) (string, []string, error) {
// TODO: maybe add a context param for cancellation, which is supported in starlark-go by
// calling thread.Cancel() from any goroutine, or maybe this doesn't matter because there is
// already a maxExecutionSteps so scripts are guaranteed to finish within a reasonable time.
// Create a Starlark thread in which the function will be called.
thread := &starlark.Thread{
Name: "starlark script executor",
Print: func(thread *starlark.Thread, msg string) {
// When the script's 'transform' function has a print(), send it to the server log.
plog.Debug("debug message while running starlark transform script", "msg", msg)
},
}
// Prevent the Starlark function from accidentally running forever.
thread.SetMaxExecutionSteps(maxExecutionSteps)
// Prepare the function arguments as Starlark values.
groupsTuple := starlark.Tuple{}
for _, group := range groups {
groupsTuple = append(groupsTuple, starlark.String(group))
}
args := starlark.Tuple{starlark.String(username), groupsTuple}
// Call the Starlark hook function in the new thread and pass the arguments.
// Get back the function's return value or an error.
hookReturnValue, err := starlark.Call(thread, t.hook, args, nil)
// Errors could be programming mistakes in the script, or could be an intentional usage of the `fail` built-in.
// Either way, return an error to reject the login.
if err != nil {
return "", nil, fmt.Errorf("error while running starlark %q function: %w", transformFunctionName, err)
}
// The special Starlark value 'None' is interpreted here as a shortcut to mean make no edits.
if hookReturnValue == starlark.None {
return username, groups, nil
}
// TODO: maybe offer a way for the user to reject a login with a nice error message which we can distinguish from
// an accidental coding error, for example by returning a single string from their 'transform' function instead
// of a tuple, or by returning a special value that we set up in the module's state in advance like
// `return rejectAuthentication(message)`
// Otherwise the function should have returned a tuple with two values.
returnedTuple, ok := hookReturnValue.(starlark.Tuple)
if !ok || returnedTuple.Len() != 2 {
return "", nil, fmt.Errorf("expected starlark %q function to return None or a Tuple of length 2", transformFunctionName)
}
// The first value in the returned tuple is the username. Turn it back into a golang string.
transformedUsername, ok := starlark.AsString(returnedTuple.Index(0))
if !ok || len(transformedUsername) == 0 {
return "", nil, fmt.Errorf("expected starlark %q function's return tuple to have a non-empty string as the first value", transformFunctionName)
}
// The second value in the returned tuple is an iterable of group names.
returnedGroups, ok := returnedTuple.Index(1).(starlark.Iterable)
if !ok {
return "", nil, fmt.Errorf("expected starlark %q function's return tuple to have an iterable value as the second value", transformFunctionName)
}
// Turn the returned iterable of group names back into a golang []string, including turning an empty iterable into an empty slice.
transformedGroupNames := []string{}
groupsIterator := returnedGroups.Iterate()
defer groupsIterator.Done()
var transformedGroup starlark.Value
for groupsIterator.Next(&transformedGroup) {
transformedGroupName, ok := starlark.AsString(transformedGroup)
if !ok || len(transformedGroupName) == 0 {
return "", nil, fmt.Errorf("expected starlark %q function's return tuple's second value to contain only non-empty strings", transformFunctionName)
}
transformedGroupNames = append(transformedGroupNames, transformedGroupName)
}
// Got username and group names, so return them as the transformed values.
return transformedUsername, transformedGroupNames, nil
}

360
internal/starformer/starformer_test.go Normal file
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@ -0,0 +1,360 @@
// Copyright 2021 the Pinniped contributors. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
package starformer
import (
"fmt"
"testing"
"time"
"github.com/stretchr/testify/require"
"go.pinniped.dev/internal/here"
)
func TestTypicalPerformance(t *testing.T) {
t.Parallel()
starformer, err := New(here.Doc(`
def transform(username, groups):
prefixedGroups = []
for g in groups:
prefixedGroups.append("group_prefix:" + g)
return "username_prefix:" + username, prefixedGroups
`))
require.NoError(t, err)
require.NotNil(t, starformer)
groups := []string{}
wantGroups := []string{}
for i := 0; i < 100; i++ {
groups = append(groups, fmt.Sprintf("g%d", i))
wantGroups = append(wantGroups, fmt.Sprintf("group_prefix:g%d", i))
}
// Before looking at performance, check that the behavior of the function is correct.
gotUsername, gotGroups, err := starformer.Transform("ryan", groups)
require.NoError(t, err)
require.Equal(t, "username_prefix:ryan", gotUsername)
require.Equal(t, wantGroups, gotGroups)
// Calling it a second time should give the same results again for the same inputs.
gotUsername, gotGroups, err = starformer.Transform("ryan", groups)
require.NoError(t, err)
require.Equal(t, "username_prefix:ryan", gotUsername)
require.Equal(t, wantGroups, gotGroups)
// This is meant to give a sense of typical runtime of a Starlark function which transforms
// a username and 100 group names. It is not meant to be a pass/fail test or scientific benchmark test.
iterations := 1000
start := time.Now()
for i := 0; i < iterations; i++ {
_, _, _ = starformer.Transform("ryan", groups)
}
elapsed := time.Since(start)
t.Logf("TestTypicalPerformance %d iteration of Transform took %s; average runtime %s", iterations, elapsed, elapsed/time.Duration(iterations))
// On my laptop this prints: TestTypicalPerformance 1000 iteration of Transform took 299.109387ms; average runtime 299.109µs
}
func TestTransformer(t *testing.T) {
// See Starlark dialect language documentation here: https://github.com/google/starlark-go/blob/master/doc/spec.md
tests := []struct {
name string
starlarkSrc string
username string
groups []string
wantUsername string
wantGroups []string
wantNewErr string
wantTransformErr string
}{
{
name: "identity function makes no modification",
starlarkSrc: here.Doc(`
def transform(username, groups):
return username, groups
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{"g1", "g2"},
},
{
name: "returning None is a shortcut for making no modification",
starlarkSrc: here.Doc(`
def transform(username, groups):
return None
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{"g1", "g2"},
},
{
name: "prefixing the username",
starlarkSrc: here.Doc(`
def transform(username, groups):
return "foobar:" + username, groups
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "foobar:ryan",
wantGroups: []string{"g1", "g2"},
},
{
name: "down-casing the username",
starlarkSrc: here.Doc(`
def transform(username, groups):
return username.lower(), groups
`),
username: "RyAn",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{"g1", "g2"},
},
{
name: "removing all groups",
starlarkSrc: here.Doc(`
def transform(username, groups):
return username, ()
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{},
},
{
name: "modifying groups",
starlarkSrc: here.Doc(`
def transform(username, groups):
return username, ("new-g1", "new-g2")
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{"new-g1", "new-g2"},
},
{
name: "converting the groups param to a list type in the business logic is easy, and returning groups as a list works",
starlarkSrc: here.Doc(`
def transform(username, groups):
groupsList = list(groups)
groupsList.pop()
return username, groupsList
`),
username: "ryan",
groups: []string{"g1", "g3"},
wantUsername: "ryan",
wantGroups: []string{"g1"},
},
{
name: "can print from the script",
starlarkSrc: here.Doc(`
print("this should get logged by Pinniped but it is not asserted here")
def transform(username, groups):
print("this should get logged by Pinniped but it is not asserted here:", username)
return username, groups
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{"g1", "g2"},
},
{
name: "rejecting a login by raising an error",
starlarkSrc: here.Doc(`
def transform(username, groups):
if username == "ryan":
fail("i don't like the username", username)
else:
return username, groups
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantTransformErr: `error while running starlark "transform" function: fail: i don't like the username ryan`,
},
{
name: "using the non-standard 'set' type is allowed",
starlarkSrc: here.Doc(`
def transform(username, groups):
groupsSet = set(groups)
if "g2" in groupsSet:
return username, groups
else:
fail("user", username, "does not belong to group g2")
`),
username: "ryan",
groups: []string{"g1", "g3"},
wantTransformErr: `error while running starlark "transform" function: fail: user ryan does not belong to group g2`,
},
{
name: "using the non-standard 'set' type is allowed, and the groups can be returned as a set",
starlarkSrc: here.Doc(`
def transform(username, groups):
groupsSet = set(groups)
groupsSet = groupsSet.union(["g42"])
if "g2" in groupsSet:
return username, groupsSet
else:
fail("user", username, "does not belong to group g2")
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{"g1", "g2", "g42"},
},
{
name: "the math module may be loaded",
starlarkSrc: here.Doc(`
load('math.star', 'math')
def transform(username, groups):
if math.round(0.4) == 0.0:
return username, groups
else:
fail("math module is supposed to work")
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{"g1", "g2"},
},
{
name: "the json module may be loaded",
starlarkSrc: here.Doc(`
load('json.star', 'json')
def transform(username, groups):
return username, [json.encode({"hello": groups[0]})]
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "ryan",
wantGroups: []string{`{"hello":"g1"}`},
},
{
name: "the time module may be loaded",
starlarkSrc: here.Doc(`
load('time.star', 'time')
def transform(username, groups):
if time.now() > time.parse_time("2001-01-20T00:00:00Z"):
return "someone", ["g3", "g4"]
fail("huh?")
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantUsername: "someone",
wantGroups: []string{"g3", "g4"},
},
{
name: "loading other modules results in an error",
starlarkSrc: here.Doc(`
load('other.star', 'other')
def transform(username, groups):
return username, groups
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantNewErr: "error while loading starlark transform script: cannot load other.star: only the following modules may be loaded: json.star, time.star, math.star",
},
{
name: "unexpected error during loading",
starlarkSrc: here.Doc(`
this is not valid starlark syntax
`),
wantNewErr: "error while loading starlark transform script: transform.star:1:8: got illegal token, want newline",
},
{
name: "too many execution steps during loading",
starlarkSrc: here.Doc(`
def helper():
a = 0
for x in range(1000000):
a += 1
helper()
`),
wantNewErr: "error while loading starlark transform script: Starlark computation cancelled: too many steps",
},
{
name: "too many execution steps during transform function",
starlarkSrc: here.Doc(`
def transform(username, groups):
a = 0
for x in range(1000000):
a += 1
return username, groups
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantTransformErr: `error while running starlark "transform" function: Starlark computation cancelled: too many steps`,
},
{
name: "returning the wrong data type",
starlarkSrc: here.Doc(`
def transform(username, groups):
return 42
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantTransformErr: `expected starlark "transform" function to return None or a Tuple of length 2`,
},
{
name: "returning the wrong data type inside the groups iterable return value",
starlarkSrc: here.Doc(`
def transform(username, groups):
return username, ("g1", 42)
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantTransformErr: `expected starlark "transform" function's return tuple's second value to contain only non-empty strings`,
},
{
name: "returning an empty string inside the groups iterable return value",
starlarkSrc: here.Doc(`
def transform(username, groups):
return username, ("g1", "", "g2")
`),
username: "ryan",
groups: []string{"g1", "g2"},
wantTransformErr: `expected starlark "transform" function's return tuple's second value to contain only non-empty strings`,
},
{
name: "no transform function defined",
starlarkSrc: here.Doc(`
def otherFunction(username, groups):
return None
`),
wantNewErr: `starlark script does not define "transform" function`,
},
{
name: "transform function defined with wrong number of positional parameters",
starlarkSrc: here.Doc(`
def transform(username):
return None
`),
wantNewErr: `starlark script's global "transform" function has 1 parameters but should have 2`,
},
}
for _, tt := range tests {
tt := tt
t.Run(tt.name, func(t *testing.T) {
t.Parallel()
starformer, err := New(tt.starlarkSrc)
if tt.wantNewErr != "" {
require.EqualError(t, err, tt.wantNewErr)
require.Nil(t, starformer)
return // wanted an error from New, so don't keep going
}
require.NoError(t, err)
require.NotNil(t, starformer)
gotUsername, gotGroups, err := starformer.Transform(tt.username, tt.groups)
if tt.wantTransformErr != "" {
require.EqualError(t, err, tt.wantTransformErr)
} else {
require.NoError(t, err)
}
require.Equal(t, tt.wantUsername, gotUsername)
require.Equal(t, tt.wantGroups, gotGroups)
})
}
}