feat: Add utility function to retrieve function credentials

example/functions/getCredentialData/README.md

@@ -0,0 +1,29 @@
+# getCredentialData
+The getCredentialData function is a utility function used to facilitate the retrieval of a function credential. Upon successful retrieval, the function returns the data of the credential. If the credential cannot be located or is unreachable, it returns nil.
+
+## Testing This Function Locally
+
+You can run your function locally and test it with [`crossplane render`](https://docs.crossplane.io/v1.18/cli/command-reference/#render/)
+
+```shell {copy-lines="1-3"}
+crossplane render xr.yaml composition.yaml functions.yaml \
+    --function-credentials=credentials.yaml \
+    --include-context
+---
+apiVersion: example.crossplane.io/v1beta1
+kind: XR
+metadata:
+  name: example
+status:
+  conditions:
+  - lastTransitionTime: "2024-01-01T00:00:00Z"
+    reason: Available
+    status: "True"
+    type: Ready
+---
+apiVersion: render.crossplane.io/v1beta1
+fields:
+  password: bar
+  username: foo
+kind: Context
+```

example/functions/getCredentialData/composition.yaml

@@ -0,0 +1,31 @@
+apiVersion: apiextensions.crossplane.io/v1
+kind: Composition
+metadata:
+  name: example-function-get-credential-data
+spec:
+  compositeTypeRef:
+    apiVersion: example.crossplane.io/v1beta1
+    kind: XR
+  mode: Pipeline
+  pipeline:
+    - step: render-templates
+      functionRef:
+        name: function-go-templating
+      credentials:
+        - name: foo-creds
+          secretRef:
+            name: foo-creds
+            namespace: default
+          source: Secret
+      input:
+        apiVersion: gotemplating.fn.crossplane.io/v1beta1
+        kind: GoTemplate
+        source: Inline
+        inline:
+          template: |
+            ---
+            apiVersion: meta.gotemplating.fn.crossplane.io/v1alpha1
+            kind: Context
+            data:
+              username: {{ ( getCredentialData . "foo-creds" ).username | toString }}
+              password: {{ ( getCredentialData . "foo-creds" ).password | toString }}

example/functions/getCredentialData/credentials.yaml

@@ -0,0 +1,9 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: foo-creds
+  namespace: default
+type: Opaque
+data:
+  username: Zm9v # foo
+  password: YmFy # bar

example/functions/getCredentialData/functions.yaml

@@ -0,0 +1,8 @@
+apiVersion: pkg.crossplane.io/v1beta1
+kind: Function
+metadata:
+  name: function-go-templating
+  annotations:
+    render.crossplane.io/runtime: Development
+spec:
+  package: xpkg.upbound.io/crossplane-contrib/function-go-templating:v0.8.0

example/functions/getCredentialData/xr.yaml

@@ -0,0 +1,5 @@
+apiVersion: example.crossplane.io/v1beta1
+kind: XR
+metadata:
+  name: example
+spec: {}

function_maps.go

@@ -12,7 +12,10 @@ import (
 	xpv1 "github.com/crossplane/crossplane-runtime/apis/common/v1"
 	"github.com/crossplane/crossplane-runtime/pkg/fieldpath"
 	"github.com/crossplane/function-sdk-go/errors"
+	fnv1 "github.com/crossplane/function-sdk-go/proto/v1"
+	"google.golang.org/protobuf/encoding/protojson"
 	"gopkg.in/yaml.v3"
+	"k8s.io/apimachinery/pkg/util/json"
 )
 
 const recursionMaxNums = 1000
@@ -26,6 +29,7 @@ var funcMaps = []template.FuncMap{
 		"setResourceNameAnnotation": setResourceNameAnnotation,
 		"getComposedResource":       getComposedResource,
 		"getCompositeResource":      getCompositeResource,
+		"getCredentialData":         getCredentialData,
 	},
 }
 
@@ -130,3 +134,34 @@ func getCompositeResource(req map[string]any) map[string]any {
 
 	return cr
 }
+
+func getCredentialData(req map[string]any, credName string) map[string][]byte {
+	credentials, err := convertFromMap(req)
+	if err != nil {
+		return nil
+	}
+
+	var data map[string][]byte
+	switch credentials.GetCredentials()[credName].GetSource().(type) {
+	case *fnv1.Credentials_CredentialData:
+		data = credentials.GetCredentials()[credName].GetCredentialData().GetData()
+	default:
+		return nil
+	}
+
+	return data
+}
+
+func convertFromMap(mReq map[string]any) (*fnv1.RunFunctionRequest, error) {
+	jReq, err := json.Marshal(&mReq)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot marshal map[string]any to json")
+	}
+
+	req := &fnv1.RunFunctionRequest{}
+	if err := protojson.Unmarshal(jReq, req); err != nil {
+		return nil, errors.Wrap(err, "cannot unmarshal request from json to proto")
+	}
+
+	return req, nil
+}

function_maps_test.go

@@ -10,6 +10,7 @@ import (
 	"google.golang.org/protobuf/testing/protocmp"
 
 	v1 "github.com/crossplane/crossplane-runtime/apis/common/v1"
+	fnv1 "github.com/crossplane/function-sdk-go/proto/v1"
 )
 
 func Test_fromYaml(t *testing.T) {
@@ -475,3 +476,62 @@ func Test_getCompositeResource(t *testing.T) {
 		})
 	}
 }
+
+func Test_getCredentialData(t *testing.T) {
+	type args struct {
+		req fnv1.RunFunctionRequest
+	}
+
+	type want struct {
+		data map[string][]byte
+	}
+
+	cases := map[string]struct {
+		reason string
+		args   args
+		want   want
+	}{
+		"RetrieveFunctionCredential": {
+			reason: "Should successfully retrieve the function credential",
+			args: args{
+				req: fnv1.RunFunctionRequest{
+					Credentials: map[string]*fnv1.Credentials{
+						"foo-creds": {
+							Source: &fnv1.Credentials_CredentialData{
+								CredentialData: &fnv1.CredentialData{
+									Data: map[string][]byte{
+										"password": []byte("secret"),
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			want: want{
+				data: map[string][]byte{
+					"password": []byte("secret"),
+				},
+			},
+		},
+		"FunctionCredentialNotFound": {
+			reason: "Should return nil if the function credential is not found",
+			args: args{
+				req: fnv1.RunFunctionRequest{
+					Credentials: map[string]*fnv1.Credentials{},
+				},
+			},
+			want: want{data: nil},
+		},
+	}
+
+	for name, tc := range cases {
+		t.Run(name, func(t *testing.T) {
+			req, _ := convertToMap(&tc.args.req)
+			got := getCredentialData(req, "foo-creds")
+			if diff := cmp.Diff(tc.want.data, got); diff != "" {
+				t.Errorf("%s\ngetCredentialData(...): -want data, +got data:\n%s", tc.reason, diff)
+			}
+		})
+	}
+}