A minimal gRPC credentials implementation for bearer tokens

LICENSE

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+MIT License
+
+Copyright (c) 2023 Andrew Benton
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+Shared libraries and tools for Go gRPC services
+
+Usage: `go get github.com/riza-io/go-grpc`
+
+#### Credentials
+
+##### Bearer tokens
+
+In your client:
+```go
+opts := []grpc.DialOption{
+    grpc.WithTransportCredentials(credentials.NewTLS(&tls.Config{})),
+    grpc.WithPerRPCCredentials(bearer.NewPerRPCCredentials("your bearer token")),
+}
+
+conn, err := grpc.Dial(hostname+":443", opts...)
+```
+
+Get a token from within your service handler:
+```go
+token, err := bearer.TokenFromContext(ctx)
+```

credentials/bearer/bearer.go

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+package bearer
+
+import (
+	"context"
+	"fmt"
+
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/metadata"
+)
+
+const (
+	mdKey          = "authorization"
+	mdValuePrefix  = "Bearer "
+	mdValueScanFmt = mdValuePrefix + "%s"
+)
+
+type Token string
+
+func (t Token) GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error) {
+	ri, _ := credentials.RequestInfoFromContext(ctx)
+	if err := credentials.CheckSecurityLevel(ri.AuthInfo, credentials.PrivacyAndIntegrity); err != nil {
+		return nil, fmt.Errorf("unable to transfer bearer.Token PerRPCCredentials: %v", err)
+	}
+	return map[string]string{
+		mdKey: mdValuePrefix + string(t),
+	}, nil
+}
+
+func (t Token) RequireTransportSecurity() bool {
+	return true
+}
+
+func NewPerRPCCredentials(token string) credentials.PerRPCCredentials {
+	return Token(token)
+}
+
+func TokenFromContext(c context.Context) (Token, error) {
+	var t Token
+	mv := metadata.ValueFromIncomingContext(c, mdKey)
+	if mv == nil || len(mv) == 0 {
+		return t, fmt.Errorf("bearer credential metadata key not found in context")
+	}
+	_, err := fmt.Sscanf(mv[0], mdValueScanFmt, &t)
+	return t, err
+}

go.mod

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+module github.com/riza-io/grpc-go
+
+go 1.17
+
+require google.golang.org/grpc v1.54.0
+
+require (
+	github.com/golang/protobuf v1.5.2 // indirect
+	google.golang.org/protobuf v1.28.1 // indirect
+)